Polymorph vortices, a monster which has a passive polymorph attack (i.e. hitting it in melee polymorphs the attacker; hitting it with missiles polymorphs the missiles) and once per turn polymorphs either one random item from its inventory, a monster it has engulfed, or a random item from that monster’s inventory. Player-style magic resistance prevents the effects to a creature or its possessions that would otherwise be affected.