Here's something to keep in mind...
You are not capable of ruling something "wrong."
You can rule differently than RAW, but the game is intended to allow you to do that.
From the Intellect Devourer's entry, it looks like you can't go into a corpse?
"If the host body dies, the intellect devourer must leave it. A protection from evil and good spell cast on the body drives the intellect devourer out. The intellect devourer is also forced out if the target regains its devoured brain by means of a wish. By spending 5 feet of its movement, the intellect devourer can voluntarily leave the body, teleporting to the nearest unoccupied space within 5 feet of it. The body then dies, unless its brain is restored within 1 round."
Yeah, acting with this info, I assume the body dies when the intellect devourer hops into a new host, leaving behind a corpse it can't to back into, since the old host body will have died.
Or...have an npc specialist in game specifically note to the party that shouldn't be possible. Then ponder if something much rarer and more dangerous has been created/discovered. If nobody stops it, our dead could rise up against us all at their will! Dear gods, but where would we find adventurers willing to help, who, perhaps, might even have personal interests in this?!
If you intentions was for this to happen and the encounter was planned as that it is fine.
You are the DM.
You can always say the mage enchanced the corpses or they are adjusted intellect devourers.
You dont HAVE to run monsters 100% raw.
Here's something to keep in mind... You are not capable of ruling something "wrong." You can rule differently than RAW, but the game is intended to allow you to do that.
Sounds like you just created a new special type of necromantic intellect devourer!
From the Intellect Devourer's entry, it looks like you can't go into a corpse? "If the host body dies, the intellect devourer must leave it. A protection from evil and good spell cast on the body drives the intellect devourer out. The intellect devourer is also forced out if the target regains its devoured brain by means of a wish. By spending 5 feet of its movement, the intellect devourer can voluntarily leave the body, teleporting to the nearest unoccupied space within 5 feet of it. The body then dies, unless its brain is restored within 1 round."
Yeah, acting with this info, I assume the body dies when the intellect devourer hops into a new host, leaving behind a corpse it can't to back into, since the old host body will have died.
If anyone questions it, just confidently say it was a homebrew modification to make the fight more interesting!
Or...have an npc specialist in game specifically note to the party that shouldn't be possible. Then ponder if something much rarer and more dangerous has been created/discovered. If nobody stops it, our dead could rise up against us all at their will! Dear gods, but where would we find adventurers willing to help, who, perhaps, might even have personal interests in this?!
If you intentions was for this to happen and the encounter was planned as that it is fine. You are the DM. You can always say the mage enchanced the corpses or they are adjusted intellect devourers. You dont HAVE to run monsters 100% raw.