The Dark Realm
The final 3 activites are found in The Dark Realm, all of which are found on the overworld and are dojos.
There are 5 bosses in the Dark Realm with Crazy Hand fought three separate times. Marx is fought in the Mysterious Dimension, Dracula is fought in Dracula's Castle, and Ganon is fought in the Sacred Land.
27 of the 73 captured fighters are unlocked in the Dark Realm. 3 of them are unlocked in the overworld, while the rest are unlocked in sub-worlds. The lists of fighters are organized roughly by order of appearance.