Don't Make Me Say It Again: I'm A Cleaner - Angrboda the Cave Elf

I recently wrapped the Mountain of the Mad Marquis, an eight session delve into one of my dungeon23 projects. At the end of the last session, when the players returned to the bottom floor to loot the aftermath of the final fight, the random encounter table spat out a single Drow riding a Tuatara. With their consumable resources exhausted, their pockets filled with other treasure, and the NPC's capabilities unknown, the players elected not to challenge her for the haul. That's the origin story of Angrboda the NPC Cave Elf, who rocketed up to Level 4 off the loot, and her trusty steed Pythia.

Goblin Punch just made a cool post about ways to apply time pressure to dungeon exploration without having to track individual torch burn rates. One of his suggestions is to shrink the value of unclaimed treasure in the dungeon each time the players go back to the surface. There are a couple ways to explain this, such as dungeon creatures carrying off the treasure, or the dungeon being a metaphysically hostile place that didn't want you to take the money out of it. I prefer the former, since it's something real the players can interact with if they realize what's happening and plan around it. DCSS had monsters like this, slimes that would hoover up items and dissolve them if you were slow exploring. They'd eat anything you left behind in the Slime Pits once you killed the boss and opened up the vault.

Let's use Angrboda as our first Cleaner, to explain where all the money went. 

ANGRBODA THE CAVE ELF
Level 4
Alignment: Chaotic
Stats: STR 9, CON 14, DEX 10, INT 9, WIS 11, CHA 5
HP: 14
AC: Chain +1 and Shield +1
Saves: D10 W11 P11 B13 S10
Attacks: Blunderbuss +1 (Damage as heavy crossbow, +4 to hit)
Silver Greataxe of Undead Bane (Damage as greataxe, +2 to hit, +5 vs Undead)
Spells Prepared: Charm Person, Knock, Sleep, Wizard LockPotions: Giant Strength, Healing, Neutralize Poison
Scrolls: Hypnotism
Magic Items: Cloak and Boots of Elvenkind, Helm of Read Languages, Tongue Stud of ESP, Lantern of Continual Light, Wand of Detect Magic
Misc Items: Rope, Grappling Hook, Tuatara Whistle, Tuatara Ball

PYTHIA THE TUATARA
Stats as Tuatara
Items Carried: Rifle+1 (Damage as heavy crossbow, range line of sight, double time to load, +1 to hit)
Potion of Water Breathing, Potion of Neutralize Poison, Potion of Healing, +1 Crossbow of Distance, Hooded Lantern of Continual Light, Crowbar, Shovel, Sledgehammer

MODUS OPERANDI

Angrboda comes from the bottom of the dungeon, while the players are probably coming from the top. This lets her sneak into rooms without encountering anyone lurking at the dungeon entrance, solving puzzles the players haven't solved yet, or clearing out dangerous monsters. She uses Knock to open doors and then Wizard Lock to close them after she's done stealing things.

Angrboda rides Pythia the Tuatara when she travels, but dismounts for stealthy work. Her Boots and Cloak of Elvenkind make her hard to spot on foot. She massively prefers to run away than fight, dashing back to the lizard and riding away into the darkness. Her wheellock blunderbus is there to blast anything that blocks her escape, she's not sticking around to reload. Pythia comes running at the sound of the shotgun.

Angrboda steals things because it's what she's always done. Hoarding arcane power was survival and a way of life in the Deep Elf colony she grew up in. As an unwanted child with no parents to inherit arcana from, her best bet was to scavenge the leftovers of the neverending duels and faction skirmishes that left the streets littered with corpses and leftover magic items. When the colony collapsed amid civil war and slave revolts, she was already a pro at pillaging leftovers. Life is extraordinarily cheap and it doesn't even occur to her that finishing off helpless victims (never dangerous ones) to take their stuff is wrong. She never harms dungeon creatures unless they block her escape. Underworld beasts are sacred to Mothermonster and Leper Heart and the other Cave Gods
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If Angrboda wants to communicate with someone, she establishes a telepathic connection with them using the tongue stud of ESP she stole off a dead hag. Usually from the other side of a sturdy wall with no nearby doors. If caught off guard by a face to face encounter she keeps her cool, giving guileless and brutally straightforward answers to questions while plotting her escape.