Ridley (Metroid)
Often considered one of the most memorable Nintendo villains, Ridley has been a mainstay of the series, having appeared (through various incarnations) in almost every "Metroid" game to date (all but "", "Metroid Prime Hunters" and ""). He has also appeared in the "Super Smash Bros." series, however, he had not been made a playable character until "Super Smash Bros. Ultimate" in 2018, making it also the first game overall to have Ridley as a playable character.
Shao Kahn
Shao Kahn and Darkseid are the key villains in the crossover game "Mortal Kombat vs. DC Universe", though both are playable characters. In the game's plot, a defeated Shao Kahn limps into a graveyard where he meets with his secret ally Quan Chi. They are confronted by Raiden, who uses a lightning bolt on Shao Kahn, which knocks him into Quan Chi’s portal. This event, along with a parallel one between Superman and Darkseid in the DC Universe, results in the creation of Dark Kahn, who serves as the main antagonist in the game. After Dark Kahn is defeated, Shao Kahn ends up in the DC Universe's Darkseid's throne room, where he discovers he has lost his powers. He is promptly imprisoned in the Phantom Zone. However, his powers came back in little time and was able to free himself but also everyone in the Phantom Zone, whom pledge allegiance to Shao Kahn.