I fixed the triggers to make it easier for you to change the ability from Divine Shield, and you can choose whether to make the ability occur when 20% HP is lost or an attack causing 20% or more damage is taken.
20% Ability
All you need to do to the ability under Techtree - Requirements is add 20% Damage Taken. Then in the Set 20 Percent Ability and Unit trigger, change Divine Shield to your ability.
20% Ability
All you need to do to the ability under Techtree - Requirements is add 20% Damage Taken. Then in the Set 20 Percent Ability and Unit trigger, change Divine Shield to your ability.
