Summon Sin Beast
Summon Beast is a monster-only spell which summons a hostile hell beast into existence. Although they aren't very dangerous individually, swarms of them can trample you around the battlefield and deal surprisingly high amounts of damage. These beasts are not worth any experience.
You can duplicate the effect of Summon Beast by blowing the horn of Geryon anywhere outside of the Vestibule of Hell; doing so will create a hostile hell beast which will immediately attack you.
The following enemies cast Summon Eyeballs:
