GAMEMODE: maybe there could be a new gamemode where there are assassins with full diamond or netherite gear (with tools) that try to kill you before you beat the ender dragon before the assassins kill you. BUT... if you look at the assasins they are frozen and they cannot move or attack the runner.
SETTING: for the new setting maybe you can change the end target for winning. So you can change it so that instead of beating the ender dragon to win, you can get a specific item or kill another mob to win. FE: you can change it so that you have to get a ghast tear or a wither skull, or you have to kill a warden and other stuff like that.