Suggest monsters for a mega-dungeon

Enworld is puking a bit with database errors and bad gateways. WE'll see if the post gets through.

Spellweaver (fiend folio) looking for something or establishing a base for some obscure reason.
Terontomorph (MM II) though it's a bit on the high side.
Yuan-ti for more intelligent areas.
Rot Reaver (MM III) which is acting as an apex predator for quick proliferating undead.
Salt mummy is an interesting less lethal variant (no disease infliction)

4e Draconomicon had a 'Dream Dragon' (or 'Nightmare Dragon?) that could be hanging out in a quiet corner, eating whatever comes by.
It could have a few scavengers nearby that dispose of the bodies after the big guy eats your mind.

Yig, Yuan Ti, Naga, Lamia Nobles, Medusa (and mix them up, so Yuan-ti/medusa & the like)

Gibberling hordes (& brood gibberlings)

Bullywugs (with lots of shamans, clerics, etc using their crazy summon monster spells)

Troglodytes

Mind flayers, grimlocks

Cythonian

Destrachan

Formless spawn, Tsathoggua

Shan(insects of Shaggi)

gibbering mouther

Lifeleech Otyugh

Choker

Phaerimm


Undead: Lich, boneclaw, deathbringer, devourer, grimwierd, heucava, mohrg, nightshades,

Kyuss critters: sons of Kyuss, Ulgurstasta +worm that walks, Avolakia
https://en.wikipedia.org/wiki/Wormspawn

Dharculus

Grell

Aboleth, Skum, etc

carrion crawlers

deep spawn

grick

Fungus(plants? in D&D): shriekers, violet, phantom, myconids

I long ago decided that abiogenesis is a fact IMC. So all vermin can appear anywhere, any time, for no reason. Same with unintelligent abberations and any similarly swarm or solitary non-intelligent magical creature. Makes it much easier to postulate dungeons. I still use a lot of constructs. Automatons are good. Caryatid columns, golems, and gargoyles. I have a huge Database of every monster book I own with info on terrain, climate, monster type, source, etc... that helps with this sort of chore. Since it has no stats in it, I would share if you like.