[Bampop]

The Wandering Monster card is not itself a fightable Monster. On the card it instructs you to play it along with a Monster card from your hand when someone (including yourself if you're looking for more Levels and Treasures) is already fighting another Monster. Narratively, the Monster from your hand was wandering around and joined the combat to help the other Monster.

If you draw it Kicking Open the Door, you add it to your hand for future use.