Can Armor stop immediate damage (such as a Grenade, Fire Trap, Lightning Blast, etc.)?
No. Immediate damage (as indicated by the burst symbol) cannot be increased or decreased by any normal means. It hits and resolves before there is the opportunity for any card play or use. See the Types of Damage box on Page 4 of the game rules. Resistance, however, can affect damage taken, including immediate damage. In the Starter Game and first three Expansion Sets, only two instances of Resistance are found: Steel Grim’s character ability of Frost Resistance and Mordol the Black’s Epic Buckler. See question #3 for more on Resistances.
