Super Mario 64
1996
Boss
Appears in three dedicated boss stages: Bowser in the Dark World (World 1), Bowser in the Fire Sea (World 2), and Bowser in the Sky (World 3/final)
Defeating him in stage 1 & 2 drops a Big Star Key, unlocking new floors of the castle. Defeating him in the final stage rewards the Power Star that saves Princess Peach and triggers the ending