What was the longest or hardest boss fight you've encountered? We're not talking about needing six tries to beat boss 1 because you forgot he had a certain move, or low level/solo challenges--this is for those bosses with annoying moves, godly amounts of HP, and usually take all your strength not to throw the controller/keyboard/handheld/phone at the wall.

Come share your war stories here! ::sparks with anticipation::