Wounds itself to prevent X city damage. Cannot prevent the first city damage dealt.
Guardian will trigger regardless of which row the unit is on.
Guardian does nothing if you take 1 city damage. If you take more than that, a Guardian unit will wound itself to prevent X city damage or reduce city damage to 1, whichever hurts more.
If you have more than one Guardian unit at a time, they will wound themselves one by one until they are all wounded or city damage is 1.
5 units have the Guardian ability: