Your question is incomplete. "Rival" could refer to several very different things:
Business Competitor: Sony (PlayStation), Microsoft (Xbox), Valve (Steam Deck), Google (Stadia — defunct), Amazon (Luna), Apple (Arcade), Tencent, NetEase, Sega (historical), Atari (historical).
Character Rival in a Nintendo Game: Wario (Mario), Dark Samus (Metroid), Wolf (Star Fox), Shadow (Sonic — Sega), Ridley (Metroid).
Developer Rival: Rare (formerly Nintendo, now Xbox), Retro Studios (Nintendo), Next Level Games (Nintendo), PlatinumGames (partner).
Console War Rival: Sega Genesis vs. SNES, PlayStation vs. N64, Xbox vs. GameCube.
Please specify:
Rival to whom/what? (Nintendo the company? Mario? Link? Pokémon?)
Domain? (Console market, mobile, specific game, character lore?)
What does "not from Nintendo" mean? (Not a Nintendo IP? Not a subsidiary? Not Japanese?)
Example: "Who is Mario's main rival not created by Nintendo?" → Sonic the Hedgehog (Sega).
