Pokemon Stadium:

 

Hyper Games:
When playing the side games, choose the scenario "Who's The Best", put it on hard mode,
with the max number of games, and win. Now you get a new mode, Hyper.

Mewtwo:
When you've defeated the Elite Four, and won every cup, Mewtwo will appear above the
Stadium. I suggest using Ice attacks to freeze him, seeing as though Psychic pokemon
are weaker against Ice, and can be frozen easily.
Submitted by: Orlandu250