Those who are healed can be unhealed in equal measure.

RIP BAND-AID

School necromancy; Level antipaladin 1, cleric 2, witch 2

Casting Time 1 standard action

Components V, S

Range close (25 ft. + 5 ft./2 levels)

Target creature healed within the last round

Duration instantaneous

Saving Throw Will half (harmless); see text; Spell Resistance yes (harmless); see text

You pervert the residual healing magic lingering within the body of the healed, causing old wounds to open and fresh blood to spill. The target takes 2d8 points of damage, or enough damage to negate the last healing effect (supernatural, arcane, or divine) cast upon them, whichever is lower.

Since undead are powered by negative energy, this spell cures such a creature of a like amount of damage caused by a healing effect that damages undead, rather than harming it. The target undead must have been damaged by a healing effect within the last round.