Bouldergiest
This boss isn't as hard as it is fun, but so many of you complain that he is hard that I simply must put him on the list, this is really a cake walk for me :D
Strategy: The strategy for this guy isn't that complicated, don't get hit. Wait for him to throw the rocks and bomb boos and when you get the chance grab 1 or 2 and fling it a bouldergiest's head then after three hits grab the bomb-boos that come out from the ground and hit him with it. His second phase just dodge his hands when ever he's about to use him. Don't be reckless, the boss can be fairly easy when you know what to do.