The series is pretty well known for good boss fights, especially in Wario Land 4 and beyond. But which game does best here and why?
This.If Wario World's an option there's no contest from me. Plenty of strange encounters with high skill ceilings that don't make me feel like I'm waiting for the boss to become vulnerable, like a certain septuple of turtles.
Limited to just the Land games, I'd go with 4. II and 3 have some great ones, but a lot of them are very limited by the games' mechanics.