Undead Damage only spell

Need a spell that harms only undead units such as holy light does, yet I don't want it to heal living units also, need it to work as an AoE. Ideas?

Unit casts a spell targeting a point
Spell equal to (Your dummy spell here)
Set life of all unit type of undead within 300 of the targeted point to -50.

Theres a field called "Unit type of ()" And inbetween the ()s is something like undead, tauren, town hall.

If you modify the spell I bet you can make it so it won't allow you to heal your own units...

Ok here is what you do

Base a spell of Holy Light. Then go to Storm Bolt, copy the Targets allowed section, then paste it in the Targets Allows spot in the custom made spell.

that's pretty intense... just modify frost nova or some other splash spell to have allowed targets be undead enemies....

Just out of curiousity, where do you see a box for Undead when looking at the window for "Targets Allowed". There is "Dead" but thats referring to actual units that have died.