This dry, partially collapsed room contains a stone altar with humanoid skulls and bones piled around it. The top of the altar is covered with dozens of half-melted candles made of black wax, all currently unlit.

Updated map -

Mal flutters to take a closer look at the altar.

Perception: 14

Zim leads the party into the new room and continues down the next hallway, to the door at the end.

Sarris is slow to pass through the 'dry' room.  Scanning about for any movement or odd(er) thing.

Passive Perception:  17

((There's still fumes in here?))

The readhead follows along with the team, relieved to get out of the water, quickly using her magic to clean her high boots up before moving on.
(Prestidigitation)

As Zim passes him the tiny invisible devil flutters ahead again to the west to scout for threats.

Another perception if needed: 5

Arkon looks around the altar room as they pass through, frowning when he notices the black candles. For some reason, Zim doesn't want any fire in here with the bad smell. The goliath pulls out his waterskin and steps over to pour some water over the unlit candles for good measure.

Zim opens the door to see another hallway, a door on one side and the hall continues on to the right. He can hear groaning come from there. 

(No fumes in this room, went high enough to avoid it.)

The altar holds nothing but the black candles. The piles of bones don't give any reaction as the party pass or even inspect it.

Updated Map -

As her imp familliar reports about what awaits the deputees down the winding corridor, Valeria quickly makes use of his senses to see for herself.
"Ahem, Zim, hold up please, we have a walking dead further down the tunnel." She says quietly while waving for Arkon and the others to catch up to face the undead together.

Perception to notice details about the undead: 11 (Is it simply the lost banite corpse from earlier?)

Meanwhile Mal stays close to the undead, ready to strike.

Zim stops once he realizes that the party is spread apart. "What's happening Val? You see something up ahead?"

"Well, there's this repulsive undead waiting for us a bit further ahead, nothing you won't cleave in twain I'm sure but perhaps Arkon and the others want to share in the fun." The redhead says quietly with a small smile.

Arkon gives a serious expression at the mention of another enemy to face, but frowns as he approaches the tunnel where the others are. "Ugh, small. It might be better if I just throw javelins from the back."

The redhead presses up against the wall to let the lumbering goliath pass. She then shrugs. "Proceed as you want Zim." She says quietly.

Gorin makes sure he catches up aswell, ready to throw Javelins too.

((is that a door at the bottom? In between Zim and Mal? Maybe ensure nothing surprises us from there?))

(Well spotted, I believe it is :-)

Zim follows Val's instructions, bringing Arkon along, behind him.

Sarris whispers to those moving forward, "Did the red head just say there was undead up ahead? "

Durak not wanting to be separated with hurry along with his companions though he waits to see if the frontliners need any help to take down the undead. 

Zim leads the train around the corner, "Where's there undead, I don't see anything."

Sarris keeps his voice low as he follows Zim and Arkon, "I can light a torch but, if the fumes are still too strong... anyway, there is a basic spell I could try but the light it creates only lasts a few seconds."

Passive Perception: 17     <<< to sniff and tell if the fumes are still too strong?