Adventurers come here to level up. You run the door, and the door charges.
Your dungeon is hired: a training ground adventurers pay to use before the real quests happen somewhere else. They pay at the door, they fight your monsters, and when their health runs out they give up and walk home. Nobody dies — a dead customer never comes back.
The monsters are stock: bought at night, used up during the day, replaced in the morning. By day you watch. By night you decide.
Google Play — soon, in closed testing.