Sponge mob

The sponge mob would be a nohostile mob floating around the ocean. Dolphins can throw the sponge around like they do with items. Sponge blocks are very hard to find unlike the sponge mob should be slightly more rare then most mobs to balance things out and not make it too easy to make sponge blocks. Sponges should drop 1-3 sponge pieces, when you 9 of those pieces you can make a sponge block.