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Allow players to change into any block in the game
(szmer.info)
That could be a funny idea though. the goal could be to survive (IE block isn't destroyed) for as long as possible (without the block being indestructible at all).
It would be a 0 player watching game after the transformation. Speedups would be very important though...
This would simplify camouflage grinders
For people who love stupid minecraft suggestions.