Lava
The Lava Shader uses a Flow Map to fade in and out between two offsets over time. Regardless of the name, you can use it also for other effects like water.. or pudding :-D
To see the lava in action, try out the Webplayer Demo.
Feel free to add a Normal Map for curvature, though you can not set Depth or Highlight tinting.
The flow map is the vital part of this shader and you can learn here how to make your own.
The intensity boosts the offset. The effect can be inverted by using negative values.
The speed in which the offset is animated, can also be inverted by using negative values.
You let the Sprite scroll by its world position, if you do not desire this behavior, just leave the scrolling values at zero. Furthermore, you can also enable Auto-Scrolling where the scrolling happens by Time.