
Stage Select:
Lynels in Breath of the Wild. It's satisfying to beat them after a hard battle. Also, they gave me a hard time in the original NES game.
I like setting God mode in classic Doom games and playing them on Nightmare difficulty, where they respawn, and setting up a bunch of infighting. The best places to do this in Doom II are Level 17, Level 18, and the Cyberdemon and Spider Mastermind in Level 20, where you can watch the four toughest monsters in the game kill each other over and over again. Usually Cybie kicks everyone else's asses and it takes them a few rounds of respawning to take him down.
The "Mover" enemies in the Northern Cave of Final Fantasy VII, mostly because you can power-level materia with them by loading the materia into your triple-growth weapons. They give out 1000 AP each.
Cage Match:
Imma go with the Easter Bunny because Cadbury Creme Eggs and Reese's Peanut Butter Eggs.