"Well, it might be looking for us now."

The model-web does have a sort of branching structure.

Can she... Hmm, she's never tried making her illusions invisible to magic senses. She will flex a mental muscle and see if it goes through, she guesses.

"Someone sketch a map, keeping this up for long will start to sting, reserves-wise."

Caron gets to work. Drawing maps quickly is an important skill for any aerial cavalry.

Meanwhile, the creepy derro necromancer cocks his head curiously. Weiss' efforts have done something to change the appearance of the illusory mists, but they haven't rendered them invisible to magic detection. 

"Hmmmmm what are creepy derro necromancers afraid of... Owlbears?"

"Alive or dead?"

"How about a paladin of Iomedae, or a dragon?"

"Derro are all insane, trying to understand and manipulate the workings of their minds is folly. Withdraw the illusion and lure him to us with it so we can ambush him, if you follow this path through the library then he'll only be able to collect the one feeding the stirges on his way."

"'kay."

The magic all rushes back towards her from every corner of the map, the mist contracting as it does. She can recover, eh, enough to be worth bothering with at least, absorbing it back into herself. She makes sure to fade it in the directed path, and moves to flank the door the derronecromancer will probably be emerging from.

The derro flies through the caves, following the receding illusion. When he reaches the stirge-tender, he speaks an order to her in an unfamiliar language. 

She crawls into one of the smaller tunnels, heading towards the two other derro playing with the rat, while the necromancer rises up and presses himself close to the ceiling of the tunnel, crawling along it in near-silence to approach the fork.

She maintains a miniature silent image depicting this to the crew. Can she interfere with the one sent to get reinforcements...? She'll try a Pretty Convincing illusory collapsed-a-while-ago tunnel, the magic used to make it so routed through solid earth... It'll smell and feel right for a 'collapsed tunnel' even and provide somewhat of an actual barrier. And she takes out the wand of Golden Chains, holding it with a ghost hand.

The best fight is the one that's over before the foe knows it's happening.

The illusion is pretty convincing! The other derro pushes against it, tries to lift one of the fallen rocks, and then gives up and doubles back to try the other small tunnel linking the otyugh pit and their sleeping area, a detour that will take her a while.

Meanwhile, the robes of the flying derro necromancer can now be glimpsed hanging down from his position as he creeps forward, about to enter vision of each other. Without the forewarning of the illusion spell, his presence up against the roof of the tunnel could easily be dismissed as shifting shadows.

She'll let the reinforcement-getter go get reinforcements on a slight deelay, and turn her whole attention to the dangerous caster.

Well, she'll wait for everyone else to be obviously ready and not strike first. Once they do strike, she'll dart into the tunnel and keep him from fleeing- By physically blocking first, and if that doesn't work, speaking the command word on the wand.

Tisharue and Oriana have taken up flanking positions on either side of the tunnel entrance, but they're waiting for a ground-level foe their weapons can reach more easily.

Vavana is the first to act. At the sight of the real robes confirms the illusory map, she crouches down and releases the spell she's been holding like a taut bowstring. A sizzling arrow of acid strikes the derro in the chest, clinging to him to painfully burn his skin and distract him from his own spellcasting.

Caron has a similar plan, readying her crossbow to shoot him as an interruption to any attempted spells.

But the screeching acid-splattered derro doesn't cast anything. Instead he spins through the air, flying forward to above the party... tearing at his clothes?

Not even the part of the robes that is covered with acid. He rips off a sleeve and throws it down?

And as the sleeve leaves his grasp, it expands and transforms mid-air into a rot-bloated ogre zombie that slams down into the back line of the party!

Okay that thing looks scary and nasty!! And is close to the squishies!!

She points the wand with the ghost hand and brushes it with her tail for the necessary contact and speaks "Lille Fai!"

Ethereal golden chains form out of nowhere with a loud sound like a bell ringing, winding tightly around every limb and the torso of the ogre zombie, and each other, some connected to the floor or trailing off into nothingness but none the less holding firm. Some of the anchor points tie parts of the body to each other with force too, making attempts to tear free of the magic with brute strength slightly self-injurious. It's the kind of thing that brute strength totally can rip through, but it ought to take at least a couple of rounds.

And then she jumps for a double-claw-strike at the derromancer.

The ogre is locked in place!

The two fighters get to work hacking at it with their swords to make sure it won't be a problem once the spell expires.

Vreeg is a challenging target, whirling in the air, and one of her claws is knocked aside by a shield of force that spins in an orbit around him. The other strike almost folds him in half, drawing blood, and he reverses direction while jabbing at Weiss with a gnarled wand like a lignified clawed hand. 

If he manages to touch her and the spell of the wand can overcome Weiss' constitution, she will find herself temporarily paralyzed.

She feels a spell slide on to her and a moment of deep dread, bracing for pain or whatever exotic effect might happen, but- It washes over and off her? Strange. Tirran spells don't really do that- Well, kind of- But she doesn't have time to think about the subtleties.

The chain pattern gold-filigree'd wand of Golden Chains falls to the floor, half-forgotten.

Necromancers. Not just any necromancer even, no, an insane necromancer, from tales of blue devils that it matches. She keeps after it, back into the tunnel it's retreating into and going for another attack.

He takes another hit, his flight becoming erratic, rips off a skirt of his robe and tosses it down to form a clattering horse skeleton obstructing the tunnel at ground level, but then exposes himself to another blow in his haste to retreat. A third strike from Weiss is enough to send him plummeting to the floor, landing heavily, on the other side of the sudden horse skeleton that is now menacing her with hoof and tooth. 

Yeah no keep rushing down the caster. Ignore the chaff and tank the damage. Even if it's taking chunks out of her lovely tail fur.

Funny how, since she didn't want to use more wand charges and also dropped it, 'hit it really hard' is the optimal strategy here.

A skeletal horse turns out to be not much of an obstacle for her, lacking the mass to be a real obstruction and unable to do more than nip at her as she passes.

Between that third blow and his hard landing, he's already unconscious, maybe dying.