I was thinking Minecraft should have an anglerfish that only spawns in deep oceans. They could have a lure that glowed and when you killed them they could have a chance of dropping that lure which could be used to make new blocks that are similar to glowstone. The anglerfish would also be hostile doing 1 heart of damage when they attacked you. The anglerfish would only be in groups of 1-2 and would have health equal to that of 3 hearts.
I really like idea and would hope it gets added to Minecraft eventually