Hola!
I published post about this Battle Rule some long ago: "Armored Up all monsters??"
And now I wanna do add a hint about it.
Do with Shield Ability ("Reduced damage from Melee and Ranged attacks") have some kind a double HP.
So if you use the Monster Card with the Shield Ability - you will have the +4 Shield HPs on it!
And the most high synergy is given by the combination "Armored Up" Battle Rule + "Shield" Ability + "Protect" Ability + "Strengthen" Ability
Of course, it should be remembered that magic ignores shields, so "Strengthen" and "Void" Abilities combination is better protected from it.
Wish you success in game with new knowledge!
Any hints from you? Please, leave them in comments!)
Join the Steem Monsters if you still have not!