Give me your most evil ideas

I’m running a one shot for a group of friends. They’re all great players and rational adults, and we love messing with and trying to outsmart one another at the table. I’m a lucky DM.

My idea is that they’re all evil aligned, level 20, retired adventurers who are summoned to their mysterious patron’s private island for the yearly game hunt. Part WWE, part Amazing Race, they’ll have to unlock seals and conquer whatever comes out of them. (The seals are actually the guardians of what’s…underneath. Probably a tarrasque).

I told them to power build. Exploit the rules of 5e to make their characters as ridiculously overpowered as possible. They’re going to throw everything they have at me, and I want to throw everything I have at them.

So let your devious minds roam - monsters, social encounters, twists, traps - help me give these lovely people a big fat middle finger. :)