To fight a monster, compare its combat strength to yours.
You and the other players may play one-shot Treasures or use Class or Race abilities to help or harm you in your combat. Some Door cards may also be played into a combat, such as monster enhancers.
Combat strength is the total of Level plus all modifiers – positive or negative – given by Items and other cards.
If the last monster is removed from a combat, it ends instantly.
Some monster cards have special powers that affect combat – a bonus against a Race or Class, for instance. Be sure to check these!