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