Passive damage bonus vs undead

I am trying to make a passive ability that when learned gives a Paladin unit a passive extra damage bonus vs undead units. There are 4 levels. 1.5x, 2x, 2.5x, 3x extra damage.

Ive tried several different things out and none of them have worked.

If there is already a thread or tutorial on this please point me in the right direction. I couldnt find one though.

Thanks for your help everyone!

Try the condition Boolean -> Unit Classification Check of Undead = True.

The problem is there is no "Undead" field in Targets allowed. You have to make some workaround. One (the most difficult) way is to completery trigger it (you will have to detect every attack, decide whether the target is undead or not and eventually add some damage accordingto the level of the skill). The other way, which comes to my mind, is to add some classification you don't use in your map (possibly suicidal if you have no kamikaze units in your map) and make an ordinary critical strike with 100% chance and "suicidal" ticked as the only field in targets allowed.

hmm i was going to suggest giving undead a seperate armor type, but if you want it as a spell with different levels i think commanderz critical strike with limited targets idea might be best.