Nergaliid

Nergaliids are rotund, scaled, frog-like devils, sometimes found in Xhorhas. According to the book The Fiends of Folklore, nergaliids were alleged to feed on people in the night while they slept. Their ability to drain life from those around them can also allow for their victims to be transformed into mutilated, zombified corpses, whose skin and muscles fell away, leaving a shambling set of bones and organs that attacked without much visible intelligence.

Kylre, a member of the Fletching and Moondrop Traveling Carnival of Curiosities, was a nergaliid posing as a lizard man until he began feeding openly.

Feeding Habits
A nergaliid has two types of feeding habits:
 * The first method is slow. The fiend siphons off the life of mortal creatures, not in such a way that it leads to harm or the death of its victim. Their victims might not even notice that it is happening to them.
 * The second method of feeding is quick and causes much pain and anguish to its victim, leaving behind corrupted, undead husks. The zombified bodies will become bestial, with their bones tearing out of the flesh to become spikes and claws, their mangled flesh turning grey, their eyes turning blood red and their faces being twisted into a permanent grimace. They become more physically powerful than they were in life, with a transformed elderly man being strong enough to tear through flesh with his fist. The zombies will immediately attempt to kill and eat at those around them, which causes the corpses of their victims to transform into more undead.

Trivia
The Nergaliid creature and stat block was created by Matthew Mercer for Critical Role.