"We'll flank it!" Oriana yells, human skeletons already dealt with. 

A few swings later, the owlbear has been damaged to the point of deanimation, collapsing back into a heap of loose bones.

"Why the Abyss does the ossuary have an owlbear?"

"Orkatto was trying to get a breeding pair for his menagerie a while back, he offered to pay for information if we saw one while flying patrol. Maybe he found one but it died and our necromancer bought the corpse?"

"Sounds like a lead, if he's not lurking down here."

She puts blue fire in her mouth and spends a bit spitting out ashes.

A line of shallow cuts along her flank is visibly closing up as she does so.

"Poor things, forced to fight after death."

"Yes, nobody likes a necromancer."

"The trail leads through the hole," Caron says, somewhat redundantly.

Along with the foxfire and Flaming sword, down the hole burrowed into the ossuary some dim light is provided by patches of mold that glow a pale blue. The air inside the rough-hewn tunnel is musty and damp, and it soon forks. Down one path Weiss can smell blood, and down the other echoes the shrieks of a rat. 

She guesses the Pharasmins will handle cleaning up the re-dead dead?

Sniff sniff.

"Blood, on the left side. Not sure how old. ...Before we get in another fight, I had a thought that I should spend a round to blind everyone with thick smoke. It takes a bit longer to do ones that keep working when I'm not looking right at them, but I can."

"Tish and I -"

"Don't call me that."

"- Tisharue and I can handle fodder like those skeletons without, no need to waste slots making them any easier, but go for it if you see anything stronger."

"Which way? I think the bodies have been dragged east, but the Small footprints are all over the place. Including..."

She guides Tisharue's sword down, illuminating a crevice to expose a much smaller tunnel, too narrow for a human to squeeze down.

"There's probably more hidden shortcuts like that. If it wasn't for the footprints not matching, I'd say kobolds."

"I hear rats, or something, down that way, and blood on the other way. Give me a minute and I can do a short ranged scry trick?"

"Do it," Vavana says immediately. 

The question of what kind of caster Weiss is can wait, there's horrible creatures creeping around tunnels so well-concealed that they could burst out into the backline and drag her away, that's any wizard's nightmare. She's sticking to Caron almost as close as she can get without clinging to her. 

Okay, so, set up the 'screen', for this she doesn't want 'camera' and the optics are annoying anyway, she can just do a sort of scale-linking thing...

Mist forms on the ground in front of her, and then a tiny scale model of the party, moving in real time, and then as she sends more and more tendrils of 'illusion' magic out, creeping along and doing nothing but feeding data to other parts of the structure- The mist populates with lines down tunnels and passages for a few hundred feet around, flood-fill into any available space more than a foot or so across. A little diorama map.

It's pretty bright to magic seeing senses, if anyone has those right now.

Vavana and Oriana are both captivated by the spell.

Down the west fork, the shrieking rat is being tormented by a pair of pale blue-skinned humanoids with wild white hair,. The presence of four straw pallets suggests that another pair are out there.

"Derros," Vavana says sourly. "Their madness makes them harder to enchant."

Why did she have to be sent on the mission where every creature would be resistant or immune to her best spells.

To the east, another derro is taking red-skinned creatures with batlike wings and mosquito-like proboscises, attaching them to a dead body that they are draining the blood from.

One tunnel from that chamber extends to the south-west, into a partially-collapsed sinkhole with water seeping in through the walls and a pile of dismembered body parts. After a short while, an otyugh tentacle emerges from the mud to take another limb to eat. 

The other exit goes into a tall hallway lined with dozens of yawning skulls. At the end, through a door that is not mistproof, is a laboratory furnished to a human scale, with three large cauldrons and stacks of alchemical equipment on the wooden tables. Another derro is cleaning up one of the cauldrons that has been toppled, spilling rendered fat onto the floor.

The laboratory pantry is boarded up. again not mistproof, and inside a vaguely humanoid monstrosity of mismatched parts from different corpses lurches about, smashing any of the spare equipment lying around that has not yet been pummeled to smithereens. 

The laboratory also has a small tunnel leading to a compact library, and a larger tunnel into a natural cavern with deep pits. In each of the three pits, a pair of human prisoners cower, while a towering man with flesh that seems to have half-melted like candlewax keeps watch.

Connected to both the library and the prisoner pits is a primitive surgical room, where the stitched monster from the pantry must have been assembled and where an incomplete new corpse-creature lies inanimate on the table, its head too small for its burly body. 

Through the surgery is an unoccupied bedroom with a desk and a mirror. Adjoining it is another bedroom, in which a fifth derro with skeleton-patterned robes experiments with a dismembered torso, making the arm thrash despite the lack of a head.  

That last derro is the only inhabitant of the warrens currently able to sense magic. He notices the mist as it spills into the room, and turns around in alarm. 

"Okay, gods. This place is a bit nasty. Regular hive of scum and villainy. Derros... Aren't necromancers, though? No, the lab is human-sized ...Uh oh, I think that one can see magic."

"I don't see why they couldn't be, madness is hardly an impediment to wizardry."

The opposite, if anything.

"Are those robes skeleton-print? That's definitely a necromancer."

The derro in question casts one spell, then another. 

He rises into the air and reorients himself horizontally like a swimmer, then glides out of his room, tracing the mist's spread backwards. His robes ripple around him like a squid's tendrils.