Witcher 3: Ghoul

A Ghoul at the beginning of the game in The Witcher 3 Wild Hunt

The Ghoul is an enemy in The Witcher 3: Wild Hunt

Ghouls are amongst the first monsters you encounter.

Description

Ghouls are hideous humanoid beasts that prey on the living and eat their corpses.

In the Prologue, during the main-quest "Lilac and Gooseberries", Geralt and Vesemir get attacked by ghouls at the start of the quest.
Encountered at the battlefield in White Orchard during the quest Missing in Action
Encountered in Velen near some pits during the quest "Funeral Pyres"

Ghouls are common and you will run into them frequently, especially at the early parts of the game.
Ghouls attack in melee
Sometimes there will be one or more Rotfiends in their group.

According to the book "Ghouls and Alghouls" written by John of Brugge, you can tell the difference between the two by markings, like unto the panthera tigris that in Zerrikania dwells, and by the sickly paleness of its visage.
After the first encounter with the Ghouls, Geralt tells Vesemir the story about a sorcerer who claimed Ghouls are useful as creatures, not because you can brew potions from their blood, but because by eating rotten corpses they prevent epidemics. Geralt and Vesemir then joke about the fact that Ghouls also eat the living.