Like other such expansion, King of Tokyo/New York: Monster Pack – Luchador consists of multiple elements that can be added to your games individually or together.
First, the monster Luchador enters the ring, with or without power cards depending on how you play King of... games.
Second, the expansion introduces "challenge mode", with each monster donning a mask at the start of play. If you damage a monster in Tokyo (or New York) and that monster doesn't retreat, you can challenge them to a one-on-one match. Each of you will play a challenge card face down, and other players can contribute challenge cards to one side of the match or the other.
Whoever pulls off the best wrestling move — a "Giant Powerhouse perhaps? — wins the match and takes the other monster's mask, which is worth 2 VP as long as you hold it.