Wahel

The first thing a dive team learns about Wahel is that everything they know about fighting zombies is wrong. Standard weaponry, the kind that puts down Shamblers and staggers Flesh Tanks, barely registers against them. Melee strikes land and do almost nothing. Firearms punch through rotting tissue and the creature keeps moving. Explosions that would scatter a pack of Gore Hounds cause only superficial harm. Wahel are not standard undead. They are something caught in the middle of becoming something worse, continuously mutating inside a Corrupted Morgue, accumulating power and Aberrant capability as they gestate. Without Wahel Bane equipment prepared by a Hell Engineer, even experienced fighters are reduced to spectators watching their own deaths approach.
  Two variants exist, and they work together with a coordination that has no right existing in dead tissue. Alpha Wahel are the fast ones: blood-drenched, feral, sprinting at full speed with elongated claws and broken teeth locked in permanent snarls. Their eyes are recessed and clouded, but the predatory focus behind them is unmistakable. They hunt in packs, converging on targets from multiple angles to deny any chance of organized defense. The second variant is the Lumbering Wahel. These are massive, misshapen things built from layers of rotting muscle and exposed connective tissue, skin stretched taut in some places and sagging in others, bloated pockets of dead tissue creating the impression of something far larger than it should be. They move at a crawl. They never stop. Every strike they land carries enough force to shatter heavy armor and drop well-equipped combatants in a handful of impacts. The Alphas swarm and saturate a team's attention while the Lumbering Wahel close the distance behind them. By the time the team realizes the slow one is in melee range, it is usually too late.
  Each individual Wahel carries a randomly assigned Aberrant Mutation, and this is what makes every dive unpredictable. An Alpha might trigger a roaring yell that heals every Wahel in the chamber and raises the ones already on the ground. Another might sniff the air and grant area awareness to the entire pack. A Lumbering Wahel might absorb an Aberrant skill used against it and throw the same skill back five times over. The mutations are invisible until they activate, and the activation is always at the worst possible moment. Dive teams learn to identify mutation carriers fast and prioritize them, because the cost of letting an Alpha Strike trigger in a room full of wounded Wahel is a room full of fully healed Wahel standing back up at once.
  What makes Wahel a concern beyond the walls of a single Corrupted Morgue is what they become when left alone. Alpha Wahel are the developmental precursor to Gore Hounds. When enough Alphas accumulate inside a Corrupted Morgue, they burst out as twenty to fifty Gore Hounds, and then the problem belongs to everyone in the settlement. An increasing concentration of Lumbering Wahel signals that the Corrupted Morgue is approaching its eruption point. At that stage, the Grave Divers are not fighting to contain a threat. They are racing to prevent a catastrophe.