Vampire Summon is a monsters-only spell which summons creatures much like the spell Summon Small Mammals. However, it summons a greater number of mammals (3-5) and replaces the harmless quokkas with dangerous orange rats.
The following enemies cast Vampire Summon:
This spell is mostly just annoying. By the time you encounter vampires, you're usually quite well prepared to handle even orange rats. rN+ can help if you really don't want to get drained, though usually if you're careful and prioritize the orange rats, you won't lose much XP anyway.
This spell was removed in 0.12.