Blood Ghoul

Ghouls subjected to great amounts of necrotic energy can twist, liquefy, and transform into sentient blobs of blood. Blood ghouls crave to siphon the blood of living creatures, drinking their life and experiences. Blood ghouls stalk through and hide in tight spaces, moving through cracks so they remain unseen until they find prey to ambush. Powerful necromancers create blood ghouls for their unique ooze like traits and great regenerative capabilities. Because of the blood ghouls being infused with great amounts of condensed necrotic energy, necromancers and other wicked creatures often use them to store that energy in one place, to be used as fuel for powerful rituals, or to siphon their great unholy energies for their own. 

Ghoul Fever.

Spread mainly through bite wounds, this rare disease makes itself known within 24 hours by swiftly debilitating the infected. A creature must make a DC 17 Constitution saving throw after every long rest. On a failed save the victim takes 14 (4d6) necrotic damage, and its hit point maximum is reduced by an amount equal to the damage taken. This reduction can’t be removed until the victim recovers from ghoul fever. A creature that has recovered from ghoul fever regains 5 of its hit point maximum after every long rest. The victim recovers from the disease by making successful saving throws on two consecutive days. Greater restoration cures the disease; lesser restoration allows the victim to make the daily Constitution check with advantage.

Primarily spread among humanoids, the disease can affect ogres, and therefore other giants may be susceptible. If the infected creature dies while infected with ghoul fever, roll 1d20, add the creature's current Constitution modifier, and find the result below to determine what undead form the victim’s body rises in:

If the creature possessed class levels in life, then it might retain them in undeath. For example, a low level spellcaster might rise as a Ghoul Mage Apprentice.