I've stumbled across a few good Sarv x Tricky crossover fics on Tumblr, honestly. It's not a massive tag, but there's a dedicated pocket of artists and writers who love throwing Hank from 'Madness Combat' into the 'Friday Night Funkin'' universe. The dynamic writes itself—Tricky's chaotic, reality-warping clown energy versus Sarv's more controlled, demonic-but-stable presence from the FNF mod. Most of the stuff I've seen leans into the absurdity, with Tricky causing mayhem in Week 7 or Sarv trying to deal with his nonsense.
Ao3 is probably your best bet for longer-form stories, though. Tags like 'Sarvente' and 'Tricky (Madness Combat)' together usually surface them. I found one called 'Devil's Bargain' that was a surprisingly thoughtful take, less about romance and more about a tense alliance between two powerful entities. The writing can be hit or miss, but when it hits, it's a fun blend of the two game's aesthetics. You might have to wade through some shorter, memeier stuff to find the real narrative gems.