D&D gives us the werewolf (at Challenge 3, it’s a little wimpy frankly, but that’s not the point). It has immunity to non-silver non-magical weaponry, which frustrates me because of how quickly it will go out of style: statistics-wise this beastie is pretty nearly an ogre, so the damage immunity is supposed to be where its additional challenge comes from. By the time we’re hitting 9th, 10th level, the party has enough spells and magical items that they’re just non-performant.
Here’s how to make them a little bit better: Werewolves don’t have their current damage immunity. Instead, while in beast and hybrid form, they have:
Regeneration If the lycanthrope has at least 1 hp at the start of its turn, it regains 10 hit points (20 during the full moon; suppressed until end of next turn if it takes radiant damage, cold damage, or damage from a silvered weapon).
Rejuvenation A slain lycanthrope reincarnates in the body of an appropriate beast within 5 miles of its gravesite at the next full moon if it isn’t buried just right (mouthful of belladonna? Powdered silver sprinkled on the grave? Whatever.).
Friendly types (werebears, swanmays, maybe others) lack these two traits entirely, and just get to shift into animal forms.
Lycanthropes continue to expose bite victims to lycanthropy, but as they only regenerate in hybrid form, so too do accursed PCs — and the evil NPC personality comes out to play in hybrid form, so a PC is actively discouraged from wolfing out. But a near-dead character might transform in order to take advantage of regeneration, flee, and then charge back into battle after a few rounds of healing!
What I like about this rules change is that you literally do have to seek a silver bullet. While magical characters can still be effective, we’re emphasizing the wizard’s cone of cold and chill touch (uncommon, interesting, that latter good against undead too); the cleric’s sacred flame and druid’s moonbeam obviously come along for the ride. I gave it radiant for moonbeam, but cold gets to come along because of its lunar associations.
This emphasizes the magical nature of the werewolf better than the existing rule, keeps them relevant for longer, and underscores that creatures with resistance and immunity to mundane damage are either impenetrable (like the gargoyle) or intangible (like the wraith); the werewolf instead is indefatiguable but still a living being (like a troll).
I’ve spoken about ghouls before too, and how little I understand their claws’ paralysis. Still true. Still confused. Grappling ghouls are fine, but can we hew closer to the book? We know that the ghoul‘s big sibling the ghast smells bad (presumably the rotting flesh and grave dirt); what if both creatures were powered by disease?
Ghoul Fever: DC 10 Constitution save or else gain this disease and the poisoned condition while diseased. Every 24 hours the victim must repeat the save; on a failure, reduce the victim’s maximum hit points by 4 (1d8), on a success, cure the disease. The hit point reduction lasts until the disease is cured. A humanoid that dies while infected rises as a ghoul the next night (or as a ghast if it lost more than 36 hit points to the disease).
This would be spread by the stench and claws of ghasts and ghouls (as appropriate); the existing stench and claw-paralysis abilities would just be transmission vectors. Elves are immune to the ghoul fever disease entirely by some quirk of their biology.
I really wanted to do keep the notion of paralysis as an effect of the disease: stunned when you take damage, for instance. But it becomes either super wordy or terrifyingly powerful; no thank you! The best I could do is something like the giant centipede’s poison: while poisoned in this way, if you are reduced to 0 hit points you are paralyzed, but that makes this ability pretty fiddly. You could also let the ghouls inflict stunning as a rider on their claws; again, quite dangerous.
Ditto, something that used filth fever’s exhaustion mechanism would be pleasing; elves don’t sleep, so there’s some teasing explanation hiding there. But unfortunately, that doesn’t work well for the ghoul’s in-combat use, and the other filth-beasts (otyugh, diseased giant rats) use a disease very similar to this one, so that’s that.
Vampires. Too large for this margin to contain.
Spirits. The big thing D&D5e has a problem with is the shadow (and the intellect devourer, maybe some others). The shadow first: it strength drains on its attacks and is nearly unique in doing so (specifically, it does 1d4 points of strength drain on each hit, lasting until the target takes a short rest). The thing that sucks about this is that it forces a few cascading effects, it’s a unique mechanism, we don’t know what stats affect what things for monsters, and we now have better mechanisms to track this anyway: exhaustion! Simply remove the strength drain from a shadow, and instead give it:
Strength drain: This is an attack. Target: 1 creature within 5 feet that breathes. The target must make a DC 12 Strength saving throw (with disadvantage if the shadow has advantage on attacks). On a failure, the target takes 9 (2d6+2) necrotic damage. Additionally, on a failure by 5 or more, the target gains one level of temporary exhaustion. Nonfatal levels of exhaustion gained in this way fade after a short or long rest. A non-evil humanoid killed by this attack spawns a shadow from their corpse after 1d4 hours.
Tadaa! Now, because there’s a saving throw here, the strong are likely to last longer; because it’s relatively low, we can stack several shadows in an encounter without it being obviously and unfairly fatal. And they ignore armor now, which is great for us; I like the idea of shadows drawing strength through breath.
The intellect devourer is not exactly a halloween monster, but while we’re here, but its fix is along the same lines. Its devour intellect becomes:
Devour Intellect: This is an attack. Target: 1 creature it can see within 10 feet that has a brain. The target must make a DC 12 Intelligence saving throw. On a failure, they take 11 (2d10) psychic damage. Additionally, on a failure by 5 or more, the target’s intelligence and charisma scores become 1. They cannot cast spells, activate magic items, understand language, or communicate in any intelligible way. They can, however, identify their friends, follow them, and even protect them. This effect ends at the end of a long rest, or via a greater restoration, heal, or wish.
Thus, the intellect devourer has to brain drain someone into unconsciousness to actually make them a valid target for Body Thief and it’s not a slam dunk they’ll have been feebleminded by then. Now, feeblemind is still awful scary to inflict, but it’s at least comparable to a cockatrice‘s petrification.