First off, Dungeon is a great start for general ambiance. Chuck in some drips and echoes from Flooded Cavern for a more natural touch, then some forge rumbles (if there’s some ancient magical forge running, 'cause why not?) from Burnt Offering’s Glassworks. Matt Mercer’s Nostoc soundset has actual working mine sounds, if you get into an active area (or an area with ghostly mining… 'cause why not?!).
Chokers - They’re fairly small, so you could use stuff from Goblin Battle, Kobold Battle, Grimple Battle, or Grioth Battle, depending on how you want to flavor your chokers.
Dark Folk - I’d use the Spooky sound set for these creepy guys, with maybe some of the Merisiel Female Rouge for knife attacks and whatnot.
Fire Environment - Fire Elemental is the obvious choice, along with again Burnt Offering’s Glassworks for a nice big ole’ forge.
Fire Drake - Red Dragon Underground, naturally.
If you’re using an actual Iron Snake (which is a great monster I love), I’d try some of the chainmail sounds from Kyra Female Cleric, rattling chains from the Skinsaw Massacre’s Following the Clues, even the clinking coins sound from Friendly Tavern. Adding in the hisses and bites from the Flying Fiend set will totally make that monster.
For the Necrophidius, you can use the hisses and bites from the Flying Fiend set again, and add in the skeleton bones and scratching bones sounds from the Zombie Battle set.
Hope that helps!
