diff --git a/data/maps/MossdeepCity_SpaceCenter_2F/scripts.inc b/data/maps/MossdeepCity_SpaceCenter_2F/scripts.inc
index 4a22bf8eeaeb..a4fcc0237cc2 100644
--- a/data/maps/MossdeepCity_SpaceCenter_2F/scripts.inc
+++ b/data/maps/MossdeepCity_SpaceCenter_2F/scripts.inc
@@ -257,14 +257,7 @@ MossdeepCity_SpaceCenter_2F_EventScript_ChoosePartyForMultiBattle::
 	goto MossdeepCity_SpaceCenter_2F_EventScript_ReadyForBattlePrompt
 
 MossdeepCity_SpaceCenter_2F_EventScript_DoStevenMultiBattle::
-	special ReducePlayerPartyToSelectedMons
-	frontier_set FRONTIER_DATA_SELECTED_MON_ORDER
-	setvar VAR_0x8004, SPECIAL_BATTLE_STEVEN
-	setvar VAR_0x8005, 0
-	special DoSpecialTrainerBattle
-	waitstate
-	frontier_saveparty
-	special LoadPlayerParty
+	multi_2_vs_2 TRAINER_MAXIE_MOSSDEEP, MossdeepCity_SpaceCenter_2F_Text_JustWantToExpandLand, TRAINER_TABITHA_MOSSDEEP, MossdeepCity_SpaceCenter_Text_TabithaDefeat, PARTNER_STEVEN, TRAINER_BACK_PIC_STEVEN
 	switch VAR_RESULT
 	case 1, MossdeepCity_SpaceCenter_2F_EventScript_DefeatedMaxieTabitha
 	fadescreen FADE_TO_BLACK
@@ -336,14 +329,6 @@ MossdeepCity_SpaceCenter_2F_EventScript_StevenFacePlayerWest::
 	turnobject LOCALID_STEVEN, DIR_EAST
 	return
 
-MossdeepCity_SpaceCenter_2F_EventScript_MaxieTrainer::
-	trainerbattle TRAINER_BATTLE_SET_TRAINER_A, TRAINER_MAXIE_MOSSDEEP, 0, MossdeepCity_SpaceCenter_2F_Text_JustWantToExpandLand, MossdeepCity_SpaceCenter_2F_Text_JustWantToExpandLand
-	end
-
-MossdeepCity_SpaceCenter_2F_EventScript_TabithaTrainer::
-	trainerbattle TRAINER_BATTLE_SET_TRAINER_B, TRAINER_TABITHA_MOSSDEEP, 0, MossdeepCity_SpaceCenter_Text_TabithaDefeat, MossdeepCity_SpaceCenter_Text_TabithaDefeat
-	end
-
 MossdeepCity_SpaceCenter_2F_EventScript_RivalRayquazaCall::
 	lockall
 	checkplayergender
diff --git a/include/constants/battle_frontier.h b/include/constants/battle_frontier.h
index 85c1df085ed4..e4a56b15d147 100644
--- a/include/constants/battle_frontier.h
+++ b/include/constants/battle_frontier.h
@@ -41,10 +41,9 @@
 #define SPECIAL_BATTLE_ARENA 5
 #define SPECIAL_BATTLE_FACTORY 6
 #define SPECIAL_BATTLE_PIKE_SINGLE 7
-#define SPECIAL_BATTLE_STEVEN 8
-#define SPECIAL_BATTLE_PIKE_DOUBLE 9
-#define SPECIAL_BATTLE_PYRAMID 10
-#define SPECIAL_BATTLE_MULTI 11
+#define SPECIAL_BATTLE_PIKE_DOUBLE 8
+#define SPECIAL_BATTLE_PYRAMID 9
+#define SPECIAL_BATTLE_MULTI 10
 
 #define MAX_BATTLE_FRONTIER_POINTS 9999
 #define MAX_STREAK 9999
diff --git a/include/constants/battle_partner.h b/include/constants/battle_partner.h
new file mode 100644
index 000000000000..5622349a888c
--- /dev/null
+++ b/include/constants/battle_partner.h
@@ -0,0 +1,8 @@
+
+#ifndef GUARD_CONSTANTS_BATTLE_PARTNERS_H
+#define GUARD_CONSTANTS_BATTLE_PARTNERS_H
+
+#define PARTNER_NONE                0
+#define PARTNER_STEVEN              1
+
+#endif  // GUARD_CONSTANTS_BATTLE_PARTNERS_H
diff --git a/include/constants/opponents.h b/include/constants/opponents.h
index c9cf9239d851..9e7131077c3b 100644
--- a/include/constants/opponents.h
+++ b/include/constants/opponents.h
@@ -1,6 +1,8 @@
 #ifndef GUARD_CONSTANTS_OPPONENTS_H
 #define GUARD_CONSTANTS_OPPONENTS_H
 
+#include "constants/battle_partner.h"
+
 #define TRAINER_NONE                          0
 #define TRAINER_SAWYER_1                      1
 #define TRAINER_GRUNT_AQUA_HIDEOUT_1          2
@@ -863,5 +865,6 @@
 
 #define TRAINERS_COUNT                      855
 #define MAX_TRAINERS_COUNT                  864
+#define TRAINER_PARTNER(partner)           (MAX_TRAINERS_COUNT + partner)
 
 #endif  // GUARD_CONSTANTS_OPPONENTS_H
diff --git a/include/constants/trainers.h b/include/constants/trainers.h
index 16904bcd1221..ff7d5b11f393 100644
--- a/include/constants/trainers.h
+++ b/include/constants/trainers.h
@@ -14,8 +14,6 @@
 #define TRAINER_SECRET_BASE                 1024
 #define TRAINER_LINK_OPPONENT               2048
 #define TRAINER_UNION_ROOM                  3072
-#define TRAINER_STEVEN_PARTNER              3075
-#define TRAINER_CUSTOM_PARTNER              3076
 
 #define TRAINER_PIC_HIKER                  0
 #define TRAINER_PIC_AQUA_GRUNT_M           1
diff --git a/include/data.h b/include/data.h
index 82b85607c0af..8fc4209d3de3 100644
--- a/include/data.h
+++ b/include/data.h
@@ -102,6 +102,8 @@ extern const struct CompressedSpriteSheet gTrainerBackPicTable[]; // functionall
 extern const struct CompressedSpritePalette gTrainerBackPicPaletteTable[];
 
 extern const struct Trainer gTrainers[];
+extern const struct Trainer gBattlePartners[];
+
 extern const u8 gTrainerClassNames[][13];
 extern const u8 gMoveNames[MOVES_COUNT_DYNAMAX][MOVE_NAME_LENGTH + 1];
 extern const u8 *const gZMoveNames[];
diff --git a/include/event_scripts.h b/include/event_scripts.h
index 00b06165cf6b..153935695900 100644
--- a/include/event_scripts.h
+++ b/include/event_scripts.h
@@ -611,7 +611,6 @@ extern const u8 EventScript_TradeCenter_Chair1[];
 extern const u8 EventScript_TradeCenter_Chair0[];
 extern const u8 EventScript_ConfirmLeaveCableClubRoom[];
 extern const u8 EventScript_TerminateLink[];
-
 extern const u8 VSSeeker_Text_BatteryNotChargedNeedXSteps[];
 extern const u8 VSSeeker_Text_NoTrainersWithinRange[];
 extern const u8 VSSeeker_Text_TrainersNotReady[];
diff --git a/src/battle_bg.c b/src/battle_bg.c
index b18962af9918..496618f3151a 100644
--- a/src/battle_bg.c
+++ b/src/battle_bg.c
@@ -26,6 +26,7 @@
 #include "constants/songs.h"
 #include "constants/trainers.h"
 #include "constants/battle_anim.h"
+#include "constants/battle_partner.h"
 
 // .rodata
 static const u16 sUnrefArray[] = {0x0300, 0x0000}; //OamData?
@@ -1146,7 +1147,7 @@ void DrawBattleEntryBackground(void)
     }
     else if (gBattleTypeFlags & (BATTLE_TYPE_FRONTIER | BATTLE_TYPE_LINK | BATTLE_TYPE_RECORDED_LINK | BATTLE_TYPE_EREADER_TRAINER))
     {
-        if (!(gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER) || gPartnerTrainerId == TRAINER_STEVEN_PARTNER || gPartnerTrainerId >= TRAINER_CUSTOM_PARTNER)
+        if (!(gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER) || gPartnerTrainerId > TRAINER_PARTNER(PARTNER_NONE))
         {
             LZDecompressVram(gBattleTerrainAnimTiles_Building, (void *)(BG_CHAR_ADDR(1)));
             LZDecompressVram(gBattleTerrainAnimTilemap_Building, (void *)(BG_SCREEN_ADDR(28)));
diff --git a/src/battle_controller_player.c b/src/battle_controller_player.c
index cf4d094fc32f..711eef1d1e93 100644
--- a/src/battle_controller_player.c
+++ b/src/battle_controller_player.c
@@ -31,6 +31,7 @@
 #include "util.h"
 #include "window.h"
 #include "constants/battle_anim.h"
+#include "constants/battle_partner.h"
 #include "constants/hold_effects.h"
 #include "constants/items.h"
 #include "constants/moves.h"
@@ -1875,7 +1876,7 @@ static void PlayerHandleDrawTrainerPic(u32 battler)
         else // First mon, on the left.
             xPos = 32;
 
-        if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER && gPartnerTrainerId != TRAINER_STEVEN_PARTNER && gPartnerTrainerId < TRAINER_CUSTOM_PARTNER)
+        if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER && gPartnerTrainerId < TRAINER_PARTNER(PARTNER_NONE))
         {
             xPos = 90;
             yPos = (8 - gTrainerFrontPicCoords[trainerPicId].size) * 4 + 80;
@@ -1893,7 +1894,7 @@ static void PlayerHandleDrawTrainerPic(u32 battler)
     }
 
     // Use front pic table for any tag battles unless your partner is Steven or a custom partner.
-    if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER && gPartnerTrainerId != TRAINER_STEVEN_PARTNER && gPartnerTrainerId < TRAINER_CUSTOM_PARTNER)
+    if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER && gPartnerTrainerId < TRAINER_PARTNER(PARTNER_NONE))
     {
         trainerPicId = PlayerGenderToFrontTrainerPicId(gSaveBlock2Ptr->playerGender);
         isFrontPic = TRUE;
diff --git a/src/battle_controller_player_partner.c b/src/battle_controller_player_partner.c
index 5155db49ec57..8f989c677d7b 100644
--- a/src/battle_controller_player_partner.c
+++ b/src/battle_controller_player_partner.c
@@ -27,6 +27,7 @@
 #include "util.h"
 #include "window.h"
 #include "constants/battle_anim.h"
+#include "constants/battle_partner.h"
 #include "constants/songs.h"
 #include "constants/party_menu.h"
 #include "constants/trainers.h"
@@ -296,15 +297,9 @@ static void PlayerPartnerHandleDrawTrainerPic(u32 battler)
     s16 xPos, yPos;
     u32 trainerPicId;
 
-    if (gPartnerTrainerId == TRAINER_STEVEN_PARTNER)
+    if (gPartnerTrainerId > TRAINER_PARTNER(PARTNER_NONE))
     {
-        trainerPicId = TRAINER_BACK_PIC_STEVEN;
-        xPos = 90;
-        yPos = (8 - gTrainerBackPicCoords[trainerPicId].size) * 4 + 80;
-    }
-    else if (gPartnerTrainerId >= TRAINER_CUSTOM_PARTNER)
-    {
-        trainerPicId = gPartnerSpriteId;
+        trainerPicId = gBattlePartners[gPartnerTrainerId - TRAINER_PARTNER(PARTNER_NONE)].trainerPic;
         xPos = 90;
         yPos = (8 - gTrainerBackPicCoords[trainerPicId].size) * 4 + 80;
     }
@@ -321,8 +316,8 @@ static void PlayerPartnerHandleDrawTrainerPic(u32 battler)
         yPos = (8 - gTrainerFrontPicCoords[trainerPicId].size) * 4 + 80;
     }
 
-    // Use back pic only if the partner is Steven or a custom partner.
-    if (gPartnerTrainerId == TRAINER_STEVEN_PARTNER || gPartnerTrainerId >= TRAINER_CUSTOM_PARTNER)
+    // Use back pic only if the partner Steven or is custom.
+    if (gPartnerTrainerId > TRAINER_PARTNER(PARTNER_NONE))
         isFrontPic = FALSE;
     else
         isFrontPic = TRUE;
@@ -439,9 +434,7 @@ static void PlayerPartnerHandleIntroTrainerBallThrow(u32 battler)
 {
     const u32 *trainerPal;
 
-    if (gPartnerTrainerId == TRAINER_STEVEN_PARTNER)
-        trainerPal = gTrainerBackPicPaletteTable[TRAINER_STEVEN_PARTNER].data;
-    else if (gPartnerTrainerId >= TRAINER_CUSTOM_PARTNER) // Custom multi battle.
+    if (gPartnerTrainerId > TRAINER_PARTNER(PARTNER_NONE))
         trainerPal = gTrainerBackPicPaletteTable[gPartnerSpriteId].data;
     else if (IsAiVsAiBattle())
         trainerPal = gTrainerFrontPicPaletteTable[gTrainers[gPartnerTrainerId].trainerPic].data;
diff --git a/src/battle_intro.c b/src/battle_intro.c
index 90ff736f003e..463804368fe9 100644
--- a/src/battle_intro.c
+++ b/src/battle_intro.c
@@ -9,6 +9,7 @@
 #include "scanline_effect.h"
 #include "task.h"
 #include "trig.h"
+#include "constants/battle_partner.h"
 #include "constants/trainers.h"
 
 extern const u8 gBattleAnimBgCntSet[];
@@ -104,7 +105,7 @@ void HandleIntroSlide(u8 terrain)
 {
     u8 taskId;
 
-    if ((gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER) && gPartnerTrainerId != TRAINER_STEVEN_PARTNER && gPartnerTrainerId < TRAINER_CUSTOM_PARTNER)
+    if ((gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER) && gPartnerTrainerId < TRAINER_PARTNER(PARTNER_NONE))
     {
         taskId = CreateTask(BattleIntroSlidePartner, 0);
     }
diff --git a/src/battle_main.c b/src/battle_main.c
index 3a81c9915730..4c28f3ffd42c 100644
--- a/src/battle_main.c
+++ b/src/battle_main.c
@@ -56,6 +56,7 @@
 #include "constants/abilities.h"
 #include "constants/battle_move_effects.h"
 #include "constants/battle_string_ids.h"
+#include "constants/battle_partner.h"
 #include "constants/hold_effects.h"
 #include "constants/items.h"
 #include "constants/moves.h"
@@ -512,7 +513,7 @@ static void CB2_InitBattleInternal(void)
 
     gBattle_WIN0H = DISPLAY_WIDTH;
 
-    if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER && gPartnerTrainerId != TRAINER_STEVEN_PARTNER && gPartnerTrainerId < TRAINER_CUSTOM_PARTNER)
+    if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER && gPartnerTrainerId < TRAINER_PARTNER(PARTNER_NONE))
     {
         gBattle_WIN0V = DISPLAY_HEIGHT - 1;
         gBattle_WIN1H = DISPLAY_WIDTH;
diff --git a/src/battle_script_commands.c b/src/battle_script_commands.c
index cebbdfb898aa..3e48794eb130 100644
--- a/src/battle_script_commands.c
+++ b/src/battle_script_commands.c
@@ -50,6 +50,7 @@
 #include "constants/battle_anim.h"
 #include "constants/battle_move_effects.h"
 #include "constants/battle_string_ids.h"
+#include "constants/battle_partner.h"
 #include "constants/hold_effects.h"
 #include "constants/items.h"
 #include "constants/item_effects.h"
@@ -4363,7 +4364,7 @@ static bool32 NoAliveMonsForPlayerAndPartner(void)
     u32 i;
     u32 HP_count = 0;
 
-    if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER && (gPartnerTrainerId == TRAINER_STEVEN_PARTNER || gPartnerTrainerId >= TRAINER_CUSTOM_PARTNER))
+    if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER && gPartnerTrainerId > TRAINER_PARTNER(PARTNER_NONE))
     {
         for (i = 0; i < PARTY_SIZE; i++)
         {
@@ -4383,25 +4384,12 @@ bool32 NoAliveMonsForPlayer(void)
     u32 i;
     u32 HP_count = 0;
 
-    // Get total HP for the player's party to determine if the player has lost
-    if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER && (gPartnerTrainerId == TRAINER_STEVEN_PARTNER || gPartnerTrainerId >= TRAINER_CUSTOM_PARTNER))
+    for (i = 0; i < PARTY_SIZE; i++)
     {
-        // In multi battle with Steven, skip his Pokémon
-        for (i = 0; i < MULTI_PARTY_SIZE; i++)
+        if (GetMonData(&gPlayerParty[i], MON_DATA_SPECIES) && !GetMonData(&gPlayerParty[i], MON_DATA_IS_EGG)
+            && (!(gBattleTypeFlags & BATTLE_TYPE_ARENA) || !(gBattleStruct->arenaLostPlayerMons & gBitTable[i])))
         {
-            if (GetMonData(&gPlayerParty[i], MON_DATA_SPECIES) && !GetMonData(&gPlayerParty[i], MON_DATA_IS_EGG))
-                HP_count += GetMonData(&gPlayerParty[i], MON_DATA_HP);
-        }
-    }
-    else
-    {
-        for (i = 0; i < PARTY_SIZE; i++)
-        {
-            if (GetMonData(&gPlayerParty[i], MON_DATA_SPECIES) && !GetMonData(&gPlayerParty[i], MON_DATA_IS_EGG)
-             && (!(gBattleTypeFlags & BATTLE_TYPE_ARENA) || !(gBattleStruct->arenaLostPlayerMons & gBitTable[i])))
-            {
-                HP_count += GetMonData(&gPlayerParty[i], MON_DATA_HP);
-            }
+            HP_count += GetMonData(&gPlayerParty[i], MON_DATA_HP);
         }
     }
 
diff --git a/src/battle_tower.c b/src/battle_tower.c
index c30406f79834..015f6d207f34 100644
--- a/src/battle_tower.c
+++ b/src/battle_tower.c
@@ -32,15 +32,13 @@
 #include "constants/battle_tent_mons.h"
 #include "constants/battle_tent_trainers.h"
 #include "constants/battle_tower.h"
+#include "constants/battle_partner.h"
 #include "constants/frontier_util.h"
 #include "constants/items.h"
 #include "constants/trainers.h"
 #include "constants/event_objects.h"
 #include "constants/moves.h"
 
-extern const u8 MossdeepCity_SpaceCenter_2F_EventScript_MaxieTrainer[];
-extern const u8 MossdeepCity_SpaceCenter_2F_EventScript_TabithaTrainer[];
-
 // EWRAM vars.
 EWRAM_DATA const struct BattleFrontierTrainer *gFacilityTrainers = NULL;
 EWRAM_DATA const struct FacilityMon *gFacilityTrainerMons = NULL;
@@ -762,44 +760,11 @@ static const u8 *const *const sPartnerApprenticeTextTables[NUM_APPRENTICES] =
     sPartnerApprenticeTexts16
 };
 
-struct
-{
-    u16 species;
-    u8 fixedIV;
-    u8 level;
-    u8 nature;
-    u8 evs[NUM_STATS];
-    u16 moves[MAX_MON_MOVES];
-} static const sStevenMons[MULTI_PARTY_SIZE] =
-{
-    {
-        .species = SPECIES_METANG,
-        .fixedIV = MAX_PER_STAT_IVS,
-        .level = 42,
-        .nature = NATURE_BRAVE,
-        .evs = {0, 252, 252, 0, 6, 0},
-        .moves = {MOVE_LIGHT_SCREEN, MOVE_PSYCHIC, MOVE_REFLECT, MOVE_METAL_CLAW}
-    },
-    {
-        .species = SPECIES_SKARMORY,
-        .fixedIV = MAX_PER_STAT_IVS,
-        .level = 43,
-        .nature = NATURE_IMPISH,
-        .evs = {252, 0, 0, 0, 6, 252},
-        .moves = {MOVE_TOXIC, MOVE_AERIAL_ACE, MOVE_PROTECT, MOVE_STEEL_WING}
-    },
-    {
-        .species = SPECIES_AGGRON,
-        .fixedIV = MAX_PER_STAT_IVS,
-        .level = 44,
-        .nature = NATURE_ADAMANT,
-        .evs = {0, 252, 0, 0, 252, 6},
-        .moves = {MOVE_THUNDER, MOVE_PROTECT, MOVE_SOLAR_BEAM, MOVE_DRAGON_CLAW}
-    }
-};
-
 #include "data/battle_frontier/battle_tent.h"
 
+#include "data/partner_parties.h"
+#include "data/battle_partners.h"
+
 static void (* const sBattleTowerFuncs[])(void) =
 {
     [BATTLE_TOWER_FUNC_INIT]                = InitTowerChallenge,
@@ -1447,13 +1412,9 @@ u8 GetFrontierOpponentClass(u16 trainerId)
     {
         return GetFrontierBrainTrainerClass();
     }
-    else if (trainerId == TRAINER_STEVEN_PARTNER)
-    {
-        trainerClass = gTrainers[TRAINER_STEVEN].trainerClass;
-    }
-    else if (trainerId >= TRAINER_CUSTOM_PARTNER)
+    else if (trainerId > TRAINER_PARTNER(PARTNER_NONE))
     {
-        trainerClass = gTrainers[trainerId - TRAINER_CUSTOM_PARTNER].trainerClass;
+        trainerClass = gBattlePartners[trainerId - TRAINER_PARTNER(PARTNER_NONE)].trainerClass;
     }
     else if (trainerId < FRONTIER_TRAINERS_COUNT)
     {
@@ -1531,15 +1492,10 @@ void GetFrontierTrainerName(u8 *dst, u16 trainerId)
         CopyFrontierBrainTrainerName(dst);
         return;
     }
-    else if (trainerId == TRAINER_STEVEN_PARTNER)
+    else if (trainerId > TRAINER_PARTNER(PARTNER_NONE))
     {
-        for (i = 0; i < PLAYER_NAME_LENGTH; i++)
-            dst[i] = gTrainers[TRAINER_STEVEN].trainerName[i];
-    }
-    else if (trainerId >= TRAINER_CUSTOM_PARTNER)
-    {
-        for (i = 0; gTrainers[trainerId - TRAINER_CUSTOM_PARTNER].trainerName[i] != EOS; i++)
-            dst[i] = gTrainers[trainerId - TRAINER_CUSTOM_PARTNER].trainerName[i];
+        for (i = 0; gBattlePartners[trainerId - TRAINER_PARTNER(PARTNER_NONE)].trainerName[i] != EOS; i++)
+            dst[i] = gBattlePartners[trainerId - TRAINER_PARTNER(PARTNER_NONE)].trainerName[i];
     }
     else if (trainerId < FRONTIER_TRAINERS_COUNT)
     {
@@ -2136,18 +2092,6 @@ void DoSpecialTrainerBattle(void)
         PlayMapChosenOrBattleBGM(0);
         BattleTransition_StartOnField(GetSpecialBattleTransition(B_TRANSITION_GROUP_B_PIKE));
         break;
-    case SPECIAL_BATTLE_STEVEN:
-        gBattleTypeFlags = BATTLE_TYPE_TRAINER | BATTLE_TYPE_DOUBLE | BATTLE_TYPE_TWO_OPPONENTS | BATTLE_TYPE_MULTI | BATTLE_TYPE_INGAME_PARTNER;
-        FillPartnerParty(TRAINER_STEVEN_PARTNER);
-        gApproachingTrainerId = 0;
-        BattleSetup_ConfigureTrainerBattle(MossdeepCity_SpaceCenter_2F_EventScript_MaxieTrainer + 1);
-        gApproachingTrainerId = 1;
-        BattleSetup_ConfigureTrainerBattle(MossdeepCity_SpaceCenter_2F_EventScript_TabithaTrainer + 1);
-        gPartnerTrainerId = TRAINER_STEVEN_PARTNER;
-        CreateTask(Task_StartBattleAfterTransition, 1);
-        PlayMapChosenOrBattleBGM(0);
-        BattleTransition_StartOnField(B_TRANSITION_MAGMA);
-        break;
     case SPECIAL_BATTLE_MULTI:
         if (gSpecialVar_0x8005 & MULTI_BATTLE_2_VS_WILD) // Player + AI against wild mon
         {
@@ -2164,7 +2108,7 @@ void DoSpecialTrainerBattle(void)
         }
 
         gPartnerSpriteId = VarGet(gSpecialVar_0x8007);
-        gPartnerTrainerId = VarGet(gSpecialVar_0x8006) + TRAINER_CUSTOM_PARTNER;
+        gPartnerTrainerId = VarGet(gSpecialVar_0x8006) + TRAINER_PARTNER(PARTNER_NONE);
         FillPartnerParty(gPartnerTrainerId);
         CreateTask(Task_StartBattleAfterTransition, 1);
         PlayMapChosenOrBattleBGM(0);
@@ -3003,7 +2947,8 @@ void TryHideBattleTowerReporter(void)
 
 static void FillPartnerParty(u16 trainerId)
 {
-    s32 i, j;
+    s32 i, j, k;
+    u32 firstIdPart = 0, secondIdPart = 0, thirdIdPart = 0;
     u32 ivs, level, personality;
     u32 friendship;
     u16 monId;
@@ -3012,47 +2957,38 @@ static void FillPartnerParty(u16 trainerId)
     s32 ball = -1;
     SetFacilityPtrsGetLevel();
 
-    if (trainerId == TRAINER_STEVEN_PARTNER)
+    if (trainerId > TRAINER_PARTNER(PARTNER_NONE))
     {
-        for (i = 0; i < MULTI_PARTY_SIZE; i++)
-        {
-            do
-            {
-                j = Random32();
-            } while (IsShinyOtIdPersonality(STEVEN_OTID, j) || sStevenMons[i].nature != GetNatureFromPersonality(j));
-            CreateMon(&gPlayerParty[MULTI_PARTY_SIZE + i],
-                      sStevenMons[i].species,
-                      sStevenMons[i].level,
-                      sStevenMons[i].fixedIV,
-                      TRUE,
-                      #ifdef BUGFIX
-                      j,
-                      #else
-                      i, // BUG: personality was stored in the 'j' variable. As a result, Steven's pokemon do not have the intended natures.
-                      #endif
-                      OT_ID_PRESET, STEVEN_OTID);
-            for (j = 0; j < PARTY_SIZE; j++)
-                SetMonData(&gPlayerParty[MULTI_PARTY_SIZE + i], MON_DATA_HP_EV + j, &sStevenMons[i].evs[j]);
-            for (j = 0; j < MAX_MON_MOVES; j++)
-                SetMonMoveSlot(&gPlayerParty[MULTI_PARTY_SIZE + i], sStevenMons[i].moves[j], j);
-            SetMonData(&gPlayerParty[MULTI_PARTY_SIZE + i], MON_DATA_OT_NAME, gTrainers[TRAINER_STEVEN].trainerName);
-            j = MALE;
-            SetMonData(&gPlayerParty[MULTI_PARTY_SIZE + i], MON_DATA_OT_GENDER, &j);
-            CalculateMonStats(&gPlayerParty[MULTI_PARTY_SIZE + i]);
-        }
-    }
-    else if (trainerId >= TRAINER_CUSTOM_PARTNER)
-    {
-        otID = Random32();
-
         for (i = 0; i < 3; i++)
             ZeroMonData(&gPlayerParty[i + 3]);
 
-        for (i = 0; i < 3 && i < gTrainers[trainerId - TRAINER_CUSTOM_PARTNER].partySize; i++)
+        for (i = 0; i < 3 && i < gBattlePartners[trainerId - TRAINER_PARTNER(PARTNER_NONE)].partySize; i++)
         {
-            const struct TrainerMon *partyData = gTrainers[trainerId - TRAINER_CUSTOM_PARTNER].party;
-            u32 otIdType = OT_ID_RANDOM_NO_SHINY;
-            do
+            const struct TrainerMon *partyData = gBattlePartners[trainerId - TRAINER_PARTNER(PARTNER_NONE)].party;
+            const u8 *partnerName = gBattlePartners[trainerId - TRAINER_PARTNER(PARTNER_NONE)].trainerName;
+
+            for (k = 0; partnerName[k] != EOS && k < 3; k++)
+            {
+                if (k == 0)
+                {
+                    firstIdPart = partnerName[k];
+                    secondIdPart = partnerName[k];
+                    thirdIdPart = partnerName[k];
+                }
+                else if (k == 1)
+                {
+                    secondIdPart = partnerName[k];
+                    thirdIdPart = partnerName[k];
+                }
+                else if (k == 2)
+                {
+                    thirdIdPart = partnerName[k];
+                }
+            }
+            if (trainerId == TRAINER_PARTNER(PARTNER_STEVEN))
+                otID = STEVEN_OTID;
+            else
+                otID = ((firstIdPart % 72) * 1000) + ((secondIdPart % 23) * 10) + (thirdIdPart % 37) % 65536;
             {
                 personality = Random32();
             } while (IsShinyOtIdPersonality(otID, personality));
@@ -3064,53 +3000,50 @@ static void FillPartnerParty(u16 trainerId)
             if (partyData[i].nature != 0)
                 ModifyPersonalityForNature(&personality, partyData[i].nature - 1);
             if (partyData[i].isShiny)
-            {
-                otIdType = OT_ID_PRESET;
-                otID = HIHALF(personality) ^ LOHALF(personality);
-            }
+                otID ^= GET_SHINY_VALUE(otID, personality) << 16;
 
-            CreateMon(&gPlayerParty[i + 3], partyData[i].species, partyData[i].lvl, 0, TRUE, personality, otIdType, otID);
+            CreateMon(&gPlayerParty[i + 3], partyData[i].species, partyData[i].lvl, 0, TRUE, personality, OT_ID_PRESET, otID);
             SetMonData(&gPlayerParty[i + 3], MON_DATA_HELD_ITEM, &partyData[i].heldItem);
-            CustomTrainerPartyAssignMoves(&gPlayerParty[i+3], &partyData[i]);
+            CustomTrainerPartyAssignMoves(&gPlayerParty[i + 3], &partyData[i]);
 
-            SetMonData(&gPlayerParty[i+3], MON_DATA_IVS, &(partyData[i].iv));
+            SetMonData(&gPlayerParty[i + 3], MON_DATA_IVS, &(partyData[i].iv));
             if (partyData[i].ev != NULL)
             {
-                SetMonData(&gPlayerParty[i+3], MON_DATA_HP_EV, &(partyData[i].ev[0]));
-                SetMonData(&gPlayerParty[i+3], MON_DATA_ATK_EV, &(partyData[i].ev[1]));
-                SetMonData(&gPlayerParty[i+3], MON_DATA_DEF_EV, &(partyData[i].ev[2]));
-                SetMonData(&gPlayerParty[i+3], MON_DATA_SPATK_EV, &(partyData[i].ev[3]));
-                SetMonData(&gPlayerParty[i+3], MON_DATA_SPDEF_EV, &(partyData[i].ev[4]));
-                SetMonData(&gPlayerParty[i+3], MON_DATA_SPEED_EV, &(partyData[i].ev[5]));
+                SetMonData(&gPlayerParty[i + 3], MON_DATA_HP_EV, &(partyData[i].ev[0]));
+                SetMonData(&gPlayerParty[i + 3], MON_DATA_ATK_EV, &(partyData[i].ev[1]));
+                SetMonData(&gPlayerParty[i + 3], MON_DATA_DEF_EV, &(partyData[i].ev[2]));
+                SetMonData(&gPlayerParty[i + 3], MON_DATA_SPATK_EV, &(partyData[i].ev[3]));
+                SetMonData(&gPlayerParty[i + 3], MON_DATA_SPDEF_EV, &(partyData[i].ev[4]));
+                SetMonData(&gPlayerParty[i + 3], MON_DATA_SPEED_EV, &(partyData[i].ev[5]));
             }
             if (partyData[i].ability != ABILITY_NONE)
             {
                 const struct SpeciesInfo *speciesInfo = &gSpeciesInfo[partyData[i].species];
                 u32 maxAbilities = ARRAY_COUNT(speciesInfo->abilities);
-                for (j = 0; j < maxAbilities; ++j)
+                for (j = 0; j < maxAbilities; j++)
                 {
                     if (speciesInfo->abilities[j] == partyData[i].ability)
                         break;
                 }
                 if (j < maxAbilities)
-                    SetMonData(&gPlayerParty[i+3], MON_DATA_ABILITY_NUM, &j);
+                    SetMonData(&gPlayerParty[i + 3], MON_DATA_ABILITY_NUM, &j);
             }
-            SetMonData(&gPlayerParty[i+3], MON_DATA_FRIENDSHIP, &(partyData[i].friendship));
+            SetMonData(&gPlayerParty[i + 3], MON_DATA_FRIENDSHIP, &(partyData[i].friendship));
             if (partyData[i].ball != ITEM_NONE)
             {
                 ball = partyData[i].ball;
-                SetMonData(&gPlayerParty[i+3], MON_DATA_POKEBALL, &ball);
+                SetMonData(&gPlayerParty[i + 3], MON_DATA_POKEBALL, &ball);
             }
             if (partyData[i].nickname != NULL)
             {
-                SetMonData(&gPlayerParty[i+3], MON_DATA_NICKNAME, partyData[i].nickname);
+                SetMonData(&gPlayerParty[i + 3], MON_DATA_NICKNAME, partyData[i].nickname);
             }
-            CalculateMonStats(&gPlayerParty[i+3]);
+            CalculateMonStats(&gPlayerParty[i + 3]);
 
-            StringCopy(trainerName, gTrainers[trainerId - TRAINER_CUSTOM_PARTNER].trainerName);
+            StringCopy(trainerName, gBattlePartners[trainerId - TRAINER_PARTNER(PARTNER_NONE)].trainerName);
             SetMonData(&gPlayerParty[i + 3], MON_DATA_OT_NAME, trainerName);
-            j = gTrainers[trainerId - TRAINER_CUSTOM_PARTNER].encounterMusic_gender >> 7;
-            SetMonData(&gPlayerParty[i+3], MON_DATA_OT_GENDER, &j);
+            j = gBattlePartners[trainerId - TRAINER_PARTNER(PARTNER_NONE)].encounterMusic_gender >> 7;
+            SetMonData(&gPlayerParty[i + 3], MON_DATA_OT_GENDER, &j);
         }
     }
     else if (trainerId == TRAINER_EREADER)
diff --git a/src/data/battle_partners.h b/src/data/battle_partners.h
new file mode 100644
index 000000000000..806a50bdf6e5
--- /dev/null
+++ b/src/data/battle_partners.h
@@ -0,0 +1,21 @@
+const struct Trainer gBattlePartners[] = {
+    [PARTNER_NONE] =
+    {
+        .party = NULL,
+        .trainerClass = TRAINER_CLASS_PKMN_TRAINER_1,
+        .encounterMusic_gender = TRAINER_ENCOUNTER_MUSIC_MALE,
+        .trainerPic = TRAINER_PIC_HIKER,
+        .trainerName = _(""),
+        .items = {},
+    },
+
+    [PARTNER_STEVEN] =
+    {
+        .party = TRAINER_PARTY(sParty_StevenPartner),
+        .trainerClass = TRAINER_CLASS_RIVAL,
+        .encounterMusic_gender = TRAINER_ENCOUNTER_MUSIC_MALE,
+        .trainerPic = TRAINER_BACK_PIC_STEVEN,
+        .trainerName = _("STEVEN"),
+    },
+
+};
diff --git a/src/data/partner_parties.h b/src/data/partner_parties.h
new file mode 100644
index 000000000000..fec80c6ca11c
--- /dev/null
+++ b/src/data/partner_parties.h
@@ -0,0 +1,26 @@
+static const struct TrainerMon sParty_StevenPartner[] = {
+    {
+        .species = SPECIES_METANG,
+        .lvl = 42,
+        .nature = TRAINER_PARTY_NATURE(NATURE_BRAVE),
+        .iv = TRAINER_PARTY_IVS(31, 31, 31, 31, 31, 31),
+        .ev = TRAINER_PARTY_EVS(0, 252, 252, 0, 6, 0),
+        .moves = {MOVE_LIGHT_SCREEN, MOVE_PSYCHIC, MOVE_REFLECT, MOVE_METAL_CLAW},
+    },
+    {
+        .species = SPECIES_SKARMORY,
+        .lvl = 43,
+        .nature = TRAINER_PARTY_NATURE(NATURE_IMPISH),
+        .iv = TRAINER_PARTY_IVS(31, 31, 31, 31, 31, 31),
+        .ev = TRAINER_PARTY_EVS(252, 0, 0, 0, 6, 252),
+        .moves = {MOVE_TOXIC, MOVE_AERIAL_ACE, MOVE_PROTECT, MOVE_STEEL_WING},
+    },
+    {
+        .species = SPECIES_AGGRON,
+        .lvl = 44,
+        .nature = TRAINER_PARTY_NATURE(NATURE_ADAMANT),
+        .iv = TRAINER_PARTY_IVS(31, 31, 31, 31, 31, 31),
+        .ev = TRAINER_PARTY_EVS(0, 252, 0, 0, 252, 6),
+        .moves = {MOVE_THUNDER, MOVE_PROTECT, MOVE_SOLAR_BEAM, MOVE_DRAGON_CLAW},
+    }
+};
diff --git a/src/pokemon.c b/src/pokemon.c
index c6b1c0dae68b..721a998bef11 100644
--- a/src/pokemon.c
+++ b/src/pokemon.c
@@ -43,6 +43,7 @@
 #include "constants/battle_frontier.h"
 #include "constants/battle_move_effects.h"
 #include "constants/battle_script_commands.h"
+#include "constants/battle_partner.h"
 #include "constants/cries.h"
 #include "constants/form_change_types.h"
 #include "constants/hold_effects.h"
@@ -858,7 +859,7 @@ void CreateBoxMon(struct BoxPokemon *boxMon, u16 species, u8 level, u8 fixedIV,
             SetBoxMonData(boxMon, MON_DATA_SPATK_IV, &iv);
             SetBoxMonData(boxMon, MON_DATA_SPDEF_IV, &iv);
         }
-        else if (P_LEGENDARY_PERFECT_IVS >= GEN_6 
+        else if (P_LEGENDARY_PERFECT_IVS >= GEN_6
          && (gSpeciesInfo[species].isLegendary
           || gSpeciesInfo[species].isMythical
           || gSpeciesInfo[species].isUltraBeast))
@@ -1824,11 +1825,11 @@ void SetMultiuseSpriteTemplateToPokemon(u16 speciesTag, u8 battlerPosition)
     gMultiuseSpriteTemplate.paletteTag = speciesTag;
     if (battlerPosition == B_POSITION_PLAYER_LEFT || battlerPosition == B_POSITION_PLAYER_RIGHT)
         gMultiuseSpriteTemplate.anims = gAnims_MonPic;
-    else 
+    else
     {
         if (speciesTag > SPECIES_SHINY_TAG)
             speciesTag = speciesTag - SPECIES_SHINY_TAG;
-        
+
         speciesTag = SanitizeSpeciesId(speciesTag);
         if (gSpeciesInfo[speciesTag].frontAnimFrames != NULL)
             gMultiuseSpriteTemplate.anims = gSpeciesInfo[speciesTag].frontAnimFrames;
@@ -5295,7 +5296,7 @@ const u8 *GetTrainerPartnerName(void)
 {
     if (gBattleTypeFlags & BATTLE_TYPE_INGAME_PARTNER)
     {
-        if (gPartnerTrainerId == TRAINER_STEVEN_PARTNER)
+        if (gPartnerTrainerId == TRAINER_PARTNER(PARTNER_STEVEN))
         {
             return gTrainers[TRAINER_STEVEN].trainerName;
         }
@@ -5518,16 +5519,22 @@ void HandleSetPokedexFlag(u16 nationalNum, u8 caseId, u32 personality)
 
 const u8 *GetTrainerClassNameFromId(u16 trainerId)
 {
-    if (trainerId >= TRAINERS_COUNT)
-        trainerId = TRAINER_NONE;
-    return gTrainerClassNames[gTrainers[trainerId].trainerClass];
+    if (trainerId > TRAINER_PARTNER(PARTNER_NONE))
+        return gTrainerClassNames[gBattlePartners[trainerId].trainerClass];
+    else if (trainerId < TRAINERS_COUNT)
+        return gTrainerClassNames[gTrainers[trainerId].trainerClass];
+
+    return gTrainerClassNames[gTrainers[TRAINER_NONE].trainerClass];
 }
 
 const u8 *GetTrainerNameFromId(u16 trainerId)
 {
-    if (trainerId >= TRAINERS_COUNT)
-        trainerId = TRAINER_NONE;
-    return gTrainers[trainerId].trainerName;
+    if (trainerId > TRAINER_PARTNER(PARTNER_NONE))
+        return gBattlePartners[trainerId].trainerName;
+    else if (trainerId < TRAINERS_COUNT)
+        return gTrainers[trainerId].trainerName;
+
+    return gTrainers[TRAINER_NONE].trainerName;
 }
 
 bool8 HasTwoFramesAnimation(u16 species)