"...Why are evil mice even a thing. What makes a mouse evil." 

"They're from Hell. They don't have evil values or evil priorities or anything but anything summoned from one of the Outer Planes will have the associated alignment."

"Weird. Sure, I can levinbolt some evil mice with Good magic and see if it hurts them but doesn't hit Hagan." 

Mahdi can summon some mice from Hell. They have forked tails for unclear reasons.

Then Vanyel will try a an underpowered Good-aligned levinbolt on both them and Hagan.

Hagan is mostly unbothered. The mice are very very bothered. 

"All right, think I'm ready to fight some fiendish vermin." Should he have a go at disabling trap-spells, or are they using the thing with the dogs again? 

They can do both, why not.

He unlocks the door first, and then tries to cut through various alarm and trap-spells, in ascending order of lethality and with the dogs a lot closer to the door than he is just in case he triggers one. 

This mostly works though the 'kick people into the future' spell goes off when cut and sends a dog into the future.

Perfect, they'll have some dogs to explore the room once it's open. "I am curious what happens to the dog two hours in the future!" he tells Mahdi. "Does the spell even last that long?" 

"It does not! Summoned creatures last a matter of minutes unless you're doing much more sophisticated stuff than I'm doing for these. I am not sure if the dog shows up for one minute several hours later or if it's just gone since by then the spell would be over."

"I guess if we're still here in two hours we could look around for a dog?" 

Does anything spring out of the room this time once the door is opened? 

Nothing springs out once the door is opened.

Can he Farsee the interior now, or get anything off mage-sight? 

There are more traps on the floor and walls. Looks like hundreds of little interlinked spells.

He gets Yfandes to bounce the mage-sight impression to the others, and describes it. "Thoughts? Does that look like 'summons fiendish vermin'?" 

"It looks like hundreds of interlinked spells each of which is going to summon one fiendish cockroach or something, at a guess. Designed like that specifically so they're a pain to disable and we'll slip up somewhere? And maybe also to hide a summons for something scarier, I'm not sure."

"That'd make sense. I'll spend a bit more time looking, see if I can pick something out of the pattern." He share his mage-senses with Yfandes as well, tries to see if there's anything behind or concealed within that mesh of little spells. 

There is a big carefully concealed trap spell that paralyzes people, probably so the fiendish cockroaches can eat them.

"How clever and horrifying. Er, I'm going to try to snip it, but might trigger it, so maybe we should have a dog nearer to it than me, just in case it goes looking for a target outside the room itself?" 

A dog can be magically obliged to go hang out nearer than them to the trap spell.

Vanyel doesn't really want to make a dog get murdered horribly even if it's summoned and will just end up back where it came from, so he looks very carefully for a place to cut that will collapse the spell on itself rather than firing it off. (It'll probably fire off the fiendish cockroach summoning spells but those seem easier to fight and possibly he can just Fetch the door shut until the summoning runs out.) 

This works! The paralysis does not trigger. The fiendish cockroaches do. They can fly, and are otherwise about as annoying as normal cockroaches.

Vanyel can...shield them, with the magic in his shield Good-aligned, and then - set them on fire? Step on them? Just blow them out of the room with a wind-spell so they can get on with it?