dalaran shield question

i have a question (as the title explains), how do i make a shield like on the second to last undead level on reign of chaos? the one that damages undead, only this time I want a shield that kills any undead unit that goes into it. I need it for my map (it includes arthas & friends) don't call me stupid. i'm new to map making but find it simpler now that i read the basics.

If you don't know how to make the graphic, it's a weather type that you can make a region have. If you don't know how to make it damage undead, I'm pretty sure it was a trigger. Such as....

Event: Unit enters region
Condition: triggering unit is undead is equal to true
Action: Kill triggering unit

That should work.

Also have that same region have its own weather, in this case Dalaron Shield