Mario and Bowser's rivalry after 30 years: Exists mostly just to uphold the status quo, instantly dissipates whenever the situation calls for it, Peach's kidnappings probably follow a very specific schedule and after every single one they all go out for coffee together. Luigi is unironically Junior's favorite babysitter.
Sonic and Eggman's rivalry after 30 years: If You So Much As Breathe In My Direction I Am Literally Going to Kill You With My Bare Hands
Link and Ganondorf’s rivalry 30 years: We are inexorably tied together by fate and ideology. We are each other’s opposite in the worst and most poetic way possible. We are enemies, we are brothers, we will destroy each other and the world around us over and over again.
Samus and Ridley’s rivalry after 30 years: BY GOD, IT’S SAMUS ARAN WITH A STEEL CHAIR!