damage reduction

[NBalfa]

How can I reduce normal damage from a unit
for example lets say that this units normal damage is 20 and we want to reduce the 10% of it.
Is there a trigger for it or maybe a system in here?
I am asking u coz I currently dont have the time for searching

 

[keychup]

Try creating a dummy unit that has Cripple on it and make it use Cripple on the unit.