I want to give the "Hardened Shield" passive ability to a custom unit having the zealot's model.
How do I achieve so?
I've made it in his Command Card as Passive, but when I start the map, it's grey'd out and not working

Add the ability to the abilities area above the Command Card?

Hardened Shield is a Behavior and not an Ability.

Adding it to the Command Card is only a cosmetic effect. You need to add the behavior to the unit.

depends how you want to activate it,

Thanks!
Solved.