How Will You Deal With Me?
"You're not supposed to be down here." the icy figure said, his armor emitting a light mist as the outer layer of ice melted and turned into water vapor. Using some Mana, the figure spread the mist further, clouding William and Carl's vision.
This was both a detection and concealment Spell, since the man could locate William and Carl based on where the water vapor didn't cover, and the mist prevented them from seeing him. Their figures became a watery outline that was easily discernable by the controller of the Spell.
What the man didn't know was that William had Life Sense Arrays embedded in his Illusionist's Cloak. When he didn't see a pair of green eyes glowing in the dark, the thief assumed that neither William nor Carl had the Life Element.