[Sandman]

The spells which summon roving indy monsters (ghost ship armada, wild hunt, that one with the three sisters) should be stripped of their global status, so they can only be stopped by beating them or recasting them yourself. They're expensive, and there aren't enough global slots to make them worthwhile.

This may not apply to the three sisters, since the spell description seems to imply that it causes insanity in blood mages worldwide. Never cast it myself, so I don't know.