Ambush

From Arkham Horror Wiki

Ambush is a monster special ability.^[1]

Once combat has begun with this creature, the investigator no longer has the option to flee it, but must instead fight until one or the other is defeated.

List of Monsters with Ambush

Monster	Expansion
Fire Vampire
Ghast
Ghoul
Leng Spider
Spectral Hunter
Tcho-tcho
Tcho-tcho Priest
Tendril of Nyogtha

References