Something like Dungeon Run, with a custom island where you can put keys into a lock to unlock an arena. Each boss has its own custom theme, and a custom item like a sword or bow, or even armor and heads. You also get Wildercoins for beating a boss, and there are challenges such as "Beat boss with no casualties." Rockets/Elytra are disabled. Each Boss would have custom armor, weapons, and effects. An endermen with a Sharp V sword, and Prot VI netherite. A fun challenge to attempt with friends for fortune and glory!