Ghouls and ghasts are a classic pair of flesh-devouring undead creatures dating all the way back to Advanced Dungeons & Dragons, ghasts being the more dangerous of the two. Unlike skeletons and zombies, which are created by necromancers casting animate dead, ghouls and ghasts are purported to have demonic origins (although there exists a spell usable by player characters, create undead, to produce them as well—here the lore and the rules contradict each other).
Both ghouls and ghasts are immune to poison and to being charmed or exhausted, and both have darkvision. They have high Dexterity and Strength, in that order, and can either claw or bite. The bite attack does more direct damage, but the claw attack has a greater chance to hit as well as a chance of paralyzing its target, rendering it incapable of action, movement or speech, granting advantage to all attacks against it, and turning all hits on it into crits. (Ghouls’ claw attack doesn’t have this effect on elves, but ghasts’ claw attack does.) Although its chances of success are low, its potential effect is so powerful that it has to be considered the attack of first resort, except against elf PCs. Finally, ghasts have the Turning Defiance feature, which grants advantage on saving throws against turning not just to themselves but to any ghoul within 30 feet of them. (They have resistance to necrotic damage, too, but that’s probably not going to be your players’ first choice against them.)
In my last article, I stated that undead creatures are driven less by survival than by compulsion—whatever compulsion the method of their creation imbues them with. In the case of ghouls and ghasts, this is hunger for the flesh of the living. This, combined with their average-level Wisdom, suggests that they possess a stronger self-preservation instinct than mindlessly obedient skeletons and zombies, since the whole point of eating is to fuel one’s continued existence. It also suggests that their goal is to obtain living flesh to eat, and that once they’ve achieved this goal, they have no particular reason to keep fighting.
Here’s the picture of ghoul combat that’s taking shape: First, since ghouls have no Stealth skill to speak of, they move in as soon as they sense the presence of potential prey. (“Potential prey” excludes elves, since they’re immune to ghouls’ paralysis.) Being driven by instinct and compulsion, they’re not daunted by being outnumbered. Therefore, they approach their chosen prey (i.e., whichever non-elf PC is closest) directly and attack with their claws. Each ghoul repeats this attack until it finally succeeds in paralyzing its prey. Once this happens, it starts snacking, switching from claws to bite and attacking with advantage, with every hit a critical. That’s 4d6 + 2 damage per bite! This is a good moment for the overly committed DM to indulge in graphic, cringe-inducing descriptions of ravenous ghouls tearing out chunks of the PCs’ muscle.
A ghoul’s victim gets to repeat its saving throw against paralysis every turn, so the ghoul wants to finish its meal as fast as it can. If a PC recovers mid-feast, the ghoul will go back to clawing the PC, hoping to paralyze him or her again.
What if another PC comes up and begins attacking the ghoul in the middle of its dinner? Rather than fight back, it will try to drag its meal away. Since the victim is completely incapacitated, not merely grappled, there’s nothing to stop the ghoul from using its full movement speed. Here, however, the ghoul faces the “eat-or-run” dilemma. Its chances of escape are best if it uses its action to Dash—and it can still carry off the paralyzed PC while doing so. But every round spent running away is a round in which dinner might wake up, and a ghoul is always hungry. Once it has a paralyzed victim, it can’t resist the compulsion to keep eating. So the ghoul will retreat from its attacker, using its full movement (and potentially incurring an opportunity attack), but then stop for another bite of its victim. In all likelihood, the PC pursuer will catch up with the ghoul and attack it again. And it will react the same way: move, then take another bite.
This cycle will repeat until one of three things happens: (a) the ghoul is reduced to 8 hp or fewer, in which case it Dashes away; (b) the ghoul is destroyed; or (c) the victim is reduced to 0 hp, in which case the ever-ravenous ghoul will turn against its erstwhile pursuer and try to make a meal of him or her. As before, it starts with claw attacks, switching to bite if and when the PC is paralyzed.
If a ghoul is shot from range while in the middle of a meal, rather than attacked hand-to-hand, it simply ignores the attack and keep eating, unless and until it’s reduced to 8 hp or fewer. Then it runs away.
The more intelligent ghast is only slightly more sophisticated. It doesn’t exempt elves from its definition of “prey,” and if it’s accompanied by a pack of ghouls, it will identify stronger PCs and direct the ghouls to gang up on them, two or three on one, depending on the relative numbers of ghasts and ghouls vs. PCs. The ghast, meanwhile, will go after a delicious elf. If the ghasts and ghouls are outnumbered by the PCs, a ghast will instead go after the strongest PC itself (being best equipped to do so, not just because of its Strength and AC but because of its Stench feature) while the ghouls go after the weaker PCs—same nutritional value, less resistance. The ghouls will always remain within 30 feet of the ghast, in order to benefit from its Turning Defiance, except when one is trying to abscond with a paralyzed victim.
Despite their greater intelligence, ghasts do have the same carnivorous compulsion as ghouls and will consequently follow the same approach to escaping with a paralyzed victim when attacked hand-to-hand. Their noxious Stench offers them some slight protection from opportunity attacks, since a PC in melee range may be poisoned by it and therefore attack with disadvantage. Also, if a ghast is hit more than once by ranged attacks or spells while consuming a victim, yet not enough to seriously wound it (reduce it to 14 hp or fewer), it will get annoyed enough to get up and go after the ranged attacker, Dashing until it can get near enough to close the gap with its normal movement, then Attack with its claws.
Next: specters, wights and wraiths.