Suggest monsters for a mega-dungeon

[Celebrim]

So, I'm doing something I haven't really done since I was a much younger DM and cared much less about consistency - populating a mega-dungeon.

I need suggestions for truly interesting monsters with little ecological impact - things you can just throw in a room for a 1000 years and still expect them alive at the end of it. Or at least, close enough to be believable.

 

[DM Howard]

I think the best way to do it would be to have the very lowest depths of the mega-dungeon to be open to your world's version of the underdark. Allowing this would create a solid foundation for a thriving ecosystem to develop within the mega-dungeon; think myconids, troglodytes, and all the other minor subterranean creatures that would find value in the seclusion and (relative) safety of a mega-dungeon type of area and then just work up the food chain! Other good choices include more magical creatures like gargoyles, oozes, and elementals as you can easily fit them outside the normal food chain. A cool idea might be to have the mega-dungeon be situated under a massive lake, and whoever built the dungeon (probably a wizard amirite?) created a series of portals that allow water to flow in controlled volumes into the dungeon at different points, thus providing a water source and potentially a minor food source with fish. You could even just make it one massive portal, so there is this huge river flowing down into this mega-dungeon, and effectively the underdark, with streams splitting off into different parts of the dungeon. But what lurks in the river? *Insert maniacal Dungeon Master laugh here*

 

[Nagol]

Obviously undead and automatons.

Molds, fungi, and slimes are great base for the ecology. An area where thermophilic organisms like brown mold grow and get farmed by more intelligent inhabitants can make an interesting contrasting area and help explain the biomass stability.

I had a lost dwarven city use this. The dwarves had been cut off for quite a while and in order to survive had a brown mold farm around a magma flow. The mold was collected by skeletons (immune to cold damage, don't radiate heat) who fed the mold to green slime and then the excess slime was killed and used for compost for fungi farms and cattle feed.

 

[Celebrim]

Obviously undead and automatons.

Obviously.

But I was hoping for something more specific.

 

[Celebrim]

I think the best way to do it would be to have the very lowest depths of the mega-dungeon to be open to your world's version of the underdark. Allowing this would create a solid foundation for a thriving ecosystem to develop within the mega-dungeon; think myconids, troglodytes, and all the other minor subterranean creatures that would find value in the seclusion and (relative) safety of a mega-dungeon type of area and then just work up the food chain! Other good choices include more magical creatures like gargoyles, oozes, and elementals as you can easily fit them outside the normal food chain. A cool idea might be to have the mega-dungeon be situated under a massive lake, and whoever built the dungeon (probably a wizard amirite?) created a series of portals that allow water to flow in controlled volumes into the dungeon at different points, thus providing a water source and potentially a minor food source with fish. You could even just make it one massive portal, so there is this huge river flowing down into this mega-dungeon, and effectively the underdark, with streams splitting off into different parts of the dungeon. But what lurks in the river? *Insert maniacal Dungeon Master laugh here*

Let's just assume for now that the map is more or less complete, and that (quite coincidentally) it has many of the features you are promoting, such as being built below a lake, having locks, canals, and valves that interconnect the levels, and having at the bottom a large living ecosystem.

Having done that, I'm now interested in populating the many otherwise empty rooms on the map where I don't have an obvious idea for what I want to put there.

 

[Nagol]

Obviously.

But I was hoping for something more specific.

Well, you haven't given a lot to base any suggestion on. Is there a theme? What's the geography like? What was in the area 1,000 years ago? Is there a preferred CR/EL range?

 

[Celebrim]

Well, you haven't given a lot to base any suggestion on. Is there a theme? What's the geography like? What was in the area 1,000 years ago? Is there a preferred CR/EL range?

Theme: The theme is largely Cthulhic, so most everything else in the dungeon is in the category of 'weird stuff'. I'm interested in monsters that are interesting tactically in of themselves, because they have interesting or unique abilities.
Geography: Imagine Mountains of Madness in the steaming hot tropics. Literally steaming, in that it is in a Yellowstone like thermoskarst area.
History: It's a ruined Cthulihic city, having been abandoned after a slave revolt.
Challenge Rating: Party is 8th-10th level. EL should be between 6 and 12 generally, but I wouldn't let this bother you, as I can basically use anything with a CR between 2 and 12.

 

[DM Howard]

Let's just assume for now that the map is more or less complete, and that (quite coincidentally) it has many of the features you are promoting, such as being built below a lake, having locks, canals, and valves that interconnect the levels, and having at the bottom a large living ecosystem.

Having done that, I'm now interested in populating the many otherwise empty rooms on the map where I don't have an obvious idea for what I want to put there.

OK, let me give it some thought. I apologize, sometimes my stream of consciousness gets away from me when my imagination takes hold.

 

[Nagol]

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)

 

[Celebrim]

Speaking of EnWorld puking