Sounds like the start of a humiliation revenge 18+ comic. Marriage, then the steamy stuff.
Bowser: Oh that felt so good Peach.
Peachio: Oh was it the best-a time you've-a ever had?
Mario then releases the possession.
Mario: Haha! So long-a Bowser! I got you! It's-a me!
Mario turns and begins to jump away happily when...
Bowser: So? You realize I still made love to Peach right? She's still here and everything! If anything you should be embarrassed for taking it that far pipe boy!
The plumber then stops in his tracks, clearly coming to a realization.
Mario: Oh no! You're-a right! I had-a sex with Bowser! ...And it was-a nice!
Bowser: Wait, what?
At this point Mario throws Cappy back onto Peach.
Peachio: You ready for round two, big-a boy?
Bowser: Uhhh...sure, but no grabbing my tail; we have a history with that.
Cappy: So this is what I've become. A glorified sex tool...