Damm i swear in god that i though of posting a simillar idie to this,
my idie is to make this spell avalabile only after a keeper looses its dungeon heart,after his minions have failled at protecting his heart the keeper shell come down to the underworld and take care of things by himself!
the call to arms spell at keeper possession will allso erase the pathetic idie of minions simply,"end their service" at you dungeon after your defeat,this will force them to fight for their lost dungeon. i sugjest that after a long period of time,after the keeper have slayed the waves of heros trying to guard their conquered dungeon,the keeper shold be able to rebuild his lost dungeon heart,thus regain control.
(i will like to make my own post about this subject,were i shold post my best idies there.)