Need help in creating a system for a player to play like a boss monster

So i want to host a oneshot i made in a group of four since the majority never played it. The only player (who lets call him doodle) played the oneshot back then with another party.

So doodle knows everything about this dungeon, i offered him to be the final boss.

İ want to implement a system where doodle can do several things in the dungeon.

Like he can teleport as the boss in the middle of combat for 2 turns. Can spawn enemies and other stuff like that, but i dont want him to abuse these. So i wanted to add something to limit him like a certain point that increase based around stuff

The game will play in a tomb of a religious figure. (The players are tomb raiders)

Tl-dr: i want to give my player a boss to control and a point system where he can redeem stuff to hinder the players. And i need help on stuff he can do and how to make him gain points.