Once sent to battle in the Planning Phase, monsters and ghosts cannot be voluntarily withdrawn (for example to avoid a nasty spell), and they have to use one of their combat options, if possible. Whether they can attack or not, they return face down. (Golems and Vampires are the exceptions – Golems always return face up. Even if your Vampire cannot attack, you may decide to return it face up. (Golems and Vampires that get turned into sheep, however, lose their abilities and are knocked out.))

Some spells force you to withdraw one or more monsters. In that case, return any affected monsters to your Monster Lair face up, as though you never sent them. You can use them in later rounds. Nothing can cause a Ghost to withdraw from the battle.