"There is no end to the number of rituals these cultists will use to twist mortal flesh. Some call the process ascension, a lie that no doubt buys them obedience. But mark my words – these abominations have not ascended. They live only to suffer and hate until they meet their final death."— Archangel Tyrael(src)
Wretched Hosts are rare, even two at a time are a rare sight, except for in Nephalem Rifts. Visually, they appear as humongous giants, broken, torn apart from the inside, with rotten skin, tentacles holding them together and becoming their weapons.
While in battle, Hosts are quite durable and can attack with their appendages in melee. Still, their real weapon is the charged-up attack that marks several spots on the ground with green glow. After a few seconds, a swarm of glowing Tomb Roaches will erupt from the Host and explode at the marked areas, dealing heavy Poison damage.
To compensate, Hosts move and attack very slowly, making it easy to outrun them and the impending Roach blasts. These blasts are also really small. While charging up, Hosts cannot perform any other actions, but can move freely after it is launched and until detonation.