Is the Mesh deform modifier supported in BGE? I'm trying to make a cube squish (like a slime) when pressing a key but Lattice is not supported in BGE, so I've used the Mesh Deform modifier using another cube as the deforming object, then I've created a shape key for the squishing animation.
But when I start the game and press the key that should start the animation, only the deforming object squishes. If the Mesh deform  is not supported as well, how can I make the cube squish?
The Mesh Deform modifier is not supported by the BGE.

You can play deforming via armature actions or shapekey actions.