(Well I don't see any reason it shouldn't work. I'm not quite sure on the physics of the hand being in water, but I think it should work.)

(Also Velmine while you are charmed, I won't be taking control of your character as stated above. 5e charmed is a lot weaker than either 3.5 or 4e. Check out the link for what you can't do while charmed.)

As the creature takes control of Velmine's mind it reads her thoughts and she can knows that it is an Aboleth. It has been badly mistreated since it's capture and imprisonment by Red Wizards, and it's hated for them is strong. You know that if you can make a Persuasive argument you might have a chance to gain an ally. (You can communicate telepathically on your turn).

Eiren attacks the creature with a skeletal hand, scoring a hit.

Baik is up 

Baik, noticing the strange nature of the attacker, who went as far as to ask Xavier why he attacked him, stays back. He’ll take the time to try and see if he can recognize the creature and it’s weaknesses, in case it decides to go on the full-fronted offense.

(Not sure what to roll for this. Add +5 for Arcana, -1 for Animal Handling, and 1 for Nature, Religion, History and Insight)

5

(well crap. I thought I’d have better luck, lol. Didn’t want to attack in case we took the ‘Nice’ route, so I decided to do that. Guess that was a waste.)

Unfortunately you don't hear anything as it was a telepathic communication. However I will allow you to see if you know anything about the creature. 

Fortunately in this case Arcana was the way to go so you luck out a little bit. Here is what you know. 

• The creature is an Aboleth 
• It can attack with both it's tentacles and with it's tail
• It can breathe both air and water 
• It can communicate telepathically, and if a creature communicates with with it telepathically it can read their deepest thoughts and desires. 
• It can enslave creatures 

Suddenly the pool surges in a tidal wave like fashion any creature within 20 feet of the pool (everyone including the mastiff) must make a DC 14 Str save or be pulled into the pool and knocked prone

Corvin, Xavier, and Velmine are up 

(Well crap, I think we’re all within 20ft)
19

Velmine Strength Save: 5

Mastiff Strength Save: 2

Quote from Pertuie >>

Velmine Strength Save: 5

Mastiff Strength Save: 2

 I guess the dice gods have taken away there blessing 🤔

You can still act (as long as you know how to swim and/or tread water)

Eiren save: 19

Str check 10

prone in the water means im in the position I need to be to swim? Or still need to spend half movement to correct myself?  Where am I at in the water?  I want to swim out and move as far from water as I can and dash to get as far away from water as possible, near or behind the black gate into that corner

Velmine 10 × 2 = R11

Mastiff 1 × 2 = N18

Xavier 9 × 4 3 = I-14

I believe that the half movement to stand up would happen as you climb out of the pool. In the spoiler are the rules on swimming.

 I'm going to say that anyone in either medium or heavy armor swimming in the water would be considered difficult terrain. And anyone wearing heavy armor will need to make a Strength (Athletics) check DC 13 or start sinking by 10 feet a round repeating the check every round to either swimming the distance you can or regain depth that you lost. 

Xavier will swim out, climb out and move to C18

Velmine (wearing light armor) attempts to move out of the water until she manages to do it by reaching T9. She gets up if possible, or otherwise dashes to get more movement and allow herself enough force to get up, still looking visibly concerned about her soaking wet clothes.

She gives the mastiff the same command of getting out of the water by dashing and getting up. It does so by moving to S20.

Then, with that all said and done, Velmine feels ready to try the pacifistic approach by exclaiming out loud and see if she can make the aberration hear her. "Hey! We don't need to fight, right, friend? No need to try to drown me? We're both trying to stop the red wizards, just work with us, and we'll all be good." And then, she uses the telepathic connection to add something else while talking to it.

(To DM's eyes only:)

Str save: 16

Corvin withstands the surging water, holding his ground.  Seeing and hearing his allies trying to reason with the creature, Corvin refrains from attacking it yet, instead moving back away from the water in case of another tidal wave (D18 maybe?  Moving west to be at least 25 feet away from the water).  "It was a bit dark for me in here," he thinks back to the creature across the telepathic link.  "We are not your foes," he continues mentally, "and we have no quarrel with you.  There is no need for us to fight."  

Persuasion? 22

Velmine make a persuasion roll with advantage 

Velmine Persuasion Check: 12

Xavier, Velmine and the mastiff all make it to shore.

Velmine's statement was meet with confusion, maybe because it didn't understand the spoken part of the message. However Corvin seems to have gotten through to the Aboleth. The Aboleth quick communicates with Corvin, Eiren and Velmine (Xavier is out of reach and Baik is invisible) that he is willing to negotiate with Corvin. Ending with "Perhaps we can come to an agreement and I won't hurt you. Do you have any spare Glyph keys I can have. I will terrorize the Red Wizards for a change, and perhaps they will agree to let me go free."

Eiren will stand down for the time being. "Well, that sounds like fun. Tell me, how would that work?"

"It's willing to negotiate," Corvin says out loud for the benefit of Xavier and Baik.  "It wants to know if we have spare glyph keys."

(Don't remember what keys we actually have.  I seemt o recall we have at least 1 or 2 duplicates didn't we?)