[RPG] What ways are there to reduce a monster’s Intelligence score

dnd-5emonsters

A School of Necromancy Wizard's Command Undead ability allows them to control an Undead creature if that creature fails a CHA saving throw, depending on the intelligence of the creature they get benefits to the save, INT 8 or higher gets advantage on the save, 12 or higher gets a save every hour.

The ability can affect Vampires but they would fall into the group that gets a saving throw every hour since they have an INT of 17, if I wanted to keep them under my control permanently I'd need to make them more dumb.

The Feeblemind spell can set their INT to 1 but they can possibly regain their INT every 30 days.
The Idiot card of a Deck of Many Things can reduce it by 1d4+1 permanently but would require 2 decks, convincing the Vampire to draw cards from it, and enough luck to draw the Idiot twice.

So what ways are there to reduce a monster's INT score? Is there a different monster that I could bargain with or control through other means that could reduce the Vampire's INT?

Best Answer

Outside of Feeblemind and Wish, the only way currently published to reduce a creature's Intelligence score is to have it be attacked by an Intellect Devourer. These appropriately named creatures have the Devour Intellect ability:

Devour Intellect. The intellect devourer targets one creature it can see within 10 feet of it that has a brain. The target must succeed on a DC 12 Intelligence saving throw against this magic or take 11 (2d10) psychic damage. Also on a failure, roll 3d6: If the total equals or exceeds the target’s Intelligence score, that score is reduced to 0. The target is stunned until it regains at least one point of Intelligence.

As well as the difficulty of getting the vampire to fail its saving throw against this ability, you will find it difficult to control an Intellect Devourer. And, of course, while this could grant you permanent control over a vampire, it would also leave that vampire permanently stunned, and therefore not a particularly useful minion.

However, technically, if you use Command Undead on the vampire while its Int is 0, and then restore its Int once it's under your control, it won't get to make a saving throw every hour.

If it fails the saving throw and has an Intelligence of 12 or higher, it can repeat the saving throw at the end of every hour until it succeeds and breaks free.

Note the present tense here - these conditions are checked when you use Command Undead. If it fails the saving throw and has an Int of 12 or higher, then it gets to make the saving throw repeatedly until it succeeds. If it failed the saving throw and has an Int of 12 or higher, it's out of luck.

This also makes Feeblemind a perfectly valid method of gaining permanent control - use Feeblemind, then use Command Undead, and it won't matter whether the vampire regains its Intelligence or not.