How can you recognize an armored enemy?

I'm trying to meet the in-game goal of killing an armoured enemy in less than five seconds. The dungeon has orcs, demons, ninjas and a treant, but there seems to be no way to tell which is armoured.

Is there a way to tell a monster is armoured? Is it up to each individual monster or is an entire class armoured? (For example, all orcs, all demons, etc.)

When you are about to start a run, and you are on the screen where you choose difficulty, see your quests etc., you also see a list of your enemies.

As I understand it, it goes Armored, Neutral, Ranged, Boss-type. So the topmost monster will be the armored one (Golem, Demon, Fallen Soldier etc.).