Baik will begin to dash to 28-G, a little disappointed he had stayed behind for safety now. He waves at the dog, hoping it’ll follow (Might not follow me since I used my action to Dash, but we can’t just leave it there.)

”Hey! Don’t just leave me here! Where’d the creature go?”

Corvin dashes after the others (I think I can reach around I26?)

Baik dashes to F30 (I calculated a little bit less than you. If you want to show how you were planning on getting to G28, I might agree with you.)

Corvin dashes to I26 (I came up with the same square.)

Baik calls the mastiff to join him and I will allow it to move on her turn. 

Velmine bag of tricks states: The creature is friendly to you and your companions, and it acts on your turn. You can use a bonus action to command how the creature moves and what action it takes on its next turn, or to give it general orders, such as to attack your enemies. In the absence of such orders, the creature acts in a fashion appropriate to its nature.

Following a friendly creature that calls it, is in a dog's (mastiff) nature. I had forgotten about that line and I will probably be a little bit more active in controlling Velmine summoned creatures if she doesn't give them orders. 

Xavier is up

Xavier will dash and move up to 24L then as a bonus action he will convert his last 3 sorcery points into a 2nd level spell slot

Xavier dashes to L24 and makes a new spell slot 

Velmine is If you don't do anything with the Mastiff it moves to G27 (as shown on the map in the spoiler below.)

Velmine gives a nod and a smile seeing the group bringing the mastiff closer in, so she decides not to worry about it. Instead, she goes after the escaped enemy by dashing quickly towards E17. Once there, she tries to go quiet, hoping she may be able to not attract attention to her on her way there.

Stealth Check: 26

Velmine dashes into the ash covered cavern. When you reach I23 you realize two things.

1. The ash is a lot thicker than you realized, as you start to wade through it at ankle deep and looks like it is going to be thigh deep for the rest of the cavern. 
2. The rough walls of the cavern make in possibly to climb vertically through the cavern The extremely rough walls make it possible to traverse the cavern horizontally without touching the floor.

Either way you choose will be different terrain. The furthest you can get moving on the ground is G22. If you decide to climb the walls you end your turn 5 feet above the ground in either F23 or I21.

Let me know what you decide. 

(Pertuie PMed me today saying that she in having an eventful mouth and may not be able to post as often. I will wait for her to post before doing the reddish creature's turn.)

The moment she feels her fit sink into the ashes she grimaces. "Oh, c'mon... I knew I should've just gone the other path and jumped through that gap in the floor..." Annoyed, but still determined, she continues, even at a slower pace (ending at G22), but otherwise takes the same course of action.

Velmine moves into the ash covered cavern. She has her back towards the chamber she just left, so she doesn't see the following. (Although she can hear.)

The reddish creature again flies across the fire vent, ending up right in front of Xavier (K,L-22,23). He stretches out a hand and touches Xavier. Xavier is very briefly engulfed in sparkling light.

Spoiler is for Xavier 

 The rest of you then hear the Reddish creature make a strange hissing noise that might or might not be a language. Gesturing behind him while making the noise. 

Xavier, Corvin, Eiren, and Baik are up 

(So the red creature isn’t attacking?)

Quote from Awaypturwpn >>

(So the red creature isn’t attacking?)

 Xavier doesn't seem to be in pain, but other than that, you need to make up your own mind as to what is happening. 

Eiren tries to decipher what's happening with the "speech," holding his attack for now since Xavier doesn't seem to be in pain.

Intelligence 11, trying to deduce if the character is casting a magical spell, or speaking in a primordial language?

Eiren believes that the sparkling light surrounding Xavier is a good indication that the creature has cast a spell. However the noise just might be a primordial language.

"What's it doing? Xavier?" Eiren holds his rapier in a guard position, still unsure.

"He is thanking of for defeating his captors and asking for our help to free his imprisoned mate. " Xavier will inform his allies.  

Addressing the creature "I have a spell to unlock, I will help."

Xavier will cast knock on the object in the next room.  

At Xavier's words Corvin stands down.

Xavier casts a knock spell and the smoke is released as if it was being held by an invisible force. Xavier can see a second reddish creature emerge from the pool of molten material. While the first one referred to it as a "her" and his mate, you can see no discernable different between the two of them. The second creature bows to Xavier and they both fly towards the north and disappear from your line of sight.

Out of combat. For ease purposes, I going to say when the reddish creature leaves, Eiren will call the party to him. Velmine leaves the ash covered cavern and the party converges on Eiren's location to figure out what to do next.

Everyone receives 2080 xp (That's inincluding the first reddish creature, but not the second, if you run into to them again they might be enemies or allies. Depending on the situation you may get Xp for the second one at some point.)

How do you want to proceed? If you want to investigate the next room you need to decide if you are going over the fire vent or through the ash covered cavern. 

Time in the Doomvault: 0 Days 14 Hours 7 Minute

Baik (25/77) - 0/1 Saving Face, 0/2 rages, 2d6/9d6 healing light, 0/1 tomb of levistus, and 1/2 fourth level spells. Hit Dice 5/8 Warlock, 0/1 Barbarian. 

Corvin (37/66) - 2/4 first level spells, 3/3 second level spell, 1/3 third level spells, 1/3 fourth level spells, 0/1 fifth level spells. 0/5 Embodiment of the Law, 0/2 Channel Divinity. Hit Dice 3/9.

Eiren (27/63) - 2/2 Bladesong, 1/1 Second Wind  0/1 Action Surge, 4/4 first level spells, 1/3 second level spells, 0/1 Blessing of the Raven Queen, 1/1 Arcana Recovery. Arrows 30 remaining (out of 40). Hit Dice: 3/7 Fighter, 2/2 Wizard. 

Velmine (34/57) -Martial Adept 0/1. Bag of Tricks 2/3, Hellish Rebuke 0/1, Darkness 0/1. Hit Dice 3/9 - [Animal Hit Points: [Mastiff: 3/3]

Xavier (42/65) -3/4 first level spells, 2/3 second level spells, 3/3 third level spells. 3/3 fourth level spells. 1/1 fifth level spells. 9/9 Sorcery Points, Healing Hands 0/1, Necrotic Shroud 0/1. Hit Dice 6/9.

 Xavier wants search the body of the wizard and then to explore the room past the vent.  How wide is the vent?  Are active flames coming through? Magical or non magical?  He has the cantrip control flames that would allow him to make 3 5 by 5 squares of flames extinguished to maybe clear a sort of path across.  He wants to avoid the ash room if possible

Xavier searches the three bodies.  The two apprentices are still frozen statues from his Cone of Cold, so he doesn't find anything on them.The Red Wizard has a pouch of gold (11gp) and a glyph key attuned to this sector (Iron Golem Founders). This is the second key you have to this sector, with Eiren holding the first one. Do you want to keep it, or give it to Corvin (who already has two glyph keys)

Moving over to investigate the fire vent, Xavier sees that it is a gout of flames about 8 feet across. The gout is fed by an exposed lava flow. (I'm not sure if control flames  will work in this case.) Xavier believes that he can jump over the vent and maybe get away with not being burnt very badly. However he doesn't thing walking through it would be a good idea.