Usurp Undead

The caster dramatically points at an undead creature within line of sight while casting the spell. If successful, the caster can issue verbal orders to the undead in question. Even if the undead creatures doesn't have ears or relies on telepathy, the caster still has verbally issue orders.   An undead creature cannot be ordered to kill itself, but it can be ordered to stand still in front of an armed opponent or to leap off a balcony.   Charisma Persistent  

Versus a Necromancer

  The spell is resisted by the Willpower of the necromancer currently controlling the undead creature in question, difficulty 7.   If the original master wins the contest , nothing happens.   If the caster gets more successes, they fully usurp control of the undead for about ten minutes per dot of the caster's Willpower.   In the event of a tie, the undead creature stops attacking or following anyone's orders for the next next two minutes. It will defend itself, use it's A-action and B-action to dodge or parry as appropriately.  

Versus a Masterless Undead

  Feral undead resist the necromancer with their WIllpower, difficulty 7. Fully free-willed undead like vampires and liches roll Willpower at difficulty 4.   If an undead creature normally lacks a Willpower score, give them a Willpower rating of 5 for the purpose of resisting this spell.   If the caster wins the contested roll, the undead has to obey the caster's commands fully for a scene. If the undead ties or beats the caster's roll, nothing happens.