Here are all of the boss fight from World 1 to the end of World 4. The Koopaling's names in the order shown are:
Wendy O. Koopa
Since this is asked a lot, here is an explanation:
Capless Mario is an easter egg, Mario has no cap while he has 99 lives. However, if you obtain 99 lives while in a level, the cap will remain until the end of the level.