Evo Pit
The pit holds twenty fighters and no exits. You arrive as a grub holding a shiv, and the only way up the chain is killing — rat duelist, hound, boar knight, ogre, troll champion, wyrm, then Pit God. Eight forms, each hitting harder and turning worse than the last, so being big is not being safe. Rounds run three minutes: farm orbs when it's crowded, pick fights you can finish, dethrone the champion before the bell. Death costs you a form or two, never the round.