Checkmate
Elimination chess tournament, featuring: Adam Warlock vs Martian Manhunter, Thanos vs Dr. Doom, Bruce Wayne vs Reed Richards, Brainiac vs Darkseid
No TP, magic, tech, or superpowers of any kind. All eight have had all knowledge of the game from their minds and are given a month to learn the game from scratch. Players know who their opponent is but don't know the identities of the other participants.