Malthius is a Special Enemy. He is the mini-boss variant of the Dark Mages, frequently found in the Chaos Expeditions, Onslaught and Incursions maps. Malthius resembles a large Dark Mage. He behaves similarly to Dark Mages, having the ability reanimate skeletons from anywhere on the map, heal himself and nearby allies, and has two ranged attacks. One of his range attacks are a fast charge quick projectile with lower damage and the other has a long charge slow speed but with heavy damage. Malthius is dangerous because he is known to fire at Cores and Sub Cores from across the map. Notably, he seems to have a higher than normal resistance to stuns.
In the Malthius Incursion he does not join the battle until Wave 5. Prior to Wave 5 he will occasionally summon Skeletons below him where the two middle lanes intersect. He summons the Healing Pads in the same locations and adds them each wave in the same pattern. The healing pads are removed the moment he joins the battle. Malthius Incursion is the only Special Enemy who drops Unique Legendary Weapons directly when slain.
Malthius is fought the same way you would fight a Dark Mage just with more health and skeletons popping up anywhere, though his long range can still become a threat if left alone. As a miniboss he has a very high amount of health.