Just an idea on slimes... I think it would be a great idea that slimes awould be able to grow to the size level above them until the reach huge. But instead of just periodicly growing they could grow when they move over something e.g. the new rotten flesh, droped by zombies; they would pick it up in the same way as the player but it would instanly increase their size. In this way you could feasibly farm slimes for the production of sticky pistons.