Board Thread:Questions and Answers/@comment-35396801-20180426200725/@comment-31763506-20180426211702

That's the old Incubus King's Armor. You find the Doom King armor in the Dark Fortress in the lead up to the Horde battle.

Skipping the Incubus King's armor dungeon in Ch 1 has no plot effect at this point. You can search the dungeon during the free roaming section of Ch 2, but you won't collect the Incubus King Armor.