Minecraft wiki entry for Slime, associated text: Entity data
Tags common to all entities[show]
Tags common to all mobs[show]
 Size: The size of the slime. Note that this value is zero-based, so 0 is the smallest slime, 1 is the next larger, etc. The sizes that spawn naturally are 0, 1, and 3. Values that are greater than 126 get clamped to 126.
 wasOnGround: 1 or 0 (true/false) - true if the slime is touching the ground.