Stanley moves 15 ft ((that's full movement now, right? Should be just at the edge of 30 ft. from S3)) NorthWest , turns and casts Witch Bolt at S3.
Attack: 8 Lightning Damage: 5 

Stanley lets loose a beam of crackling, blue energy that lances out toward a Sahuagin 3, forming a sustained arc of lightning between him and the it. S3 takes 9 Lightning damage. 

It is now all of the enemies' turns.

Updated Map - Round 5, Turns 5-10 - Beginning of the Enemies' Turns

When Stanley attacked Selachai, that triggered Usul's held attack and the bolt flies towards S3, but it misses.

Selachai moves her full 40' back to where she was before Darla's psychic attack and casts an eldritch blast at Snurk:

• Attack: 12 Damage: 2 force damage
• She misses him

Sahuagin 1 also goes in for a multi-attack (one bite and one slash w/claws) vs Snurk:

• Attack: 15 Damage: 5 piercing damage
• Attack: 4 Damage: 2 slashing damage
• I forgot to make these attacks at disadvantage due to Snurk's Dodge action, so I had to re-roll them and they both missed.

Sahuagin 2 moves SE 5' and attacks Snurk with a multi-attack (at disadvantage):

• Attack: 9 Damage: 3 piercing damage
• Attack: 17 Damage: 5 slashing damage
• S2 succeeds at hitting Snurk with his claws, making skin contact and requiring a DC12 CON save for poison: 20 - he avoids becoming poisoned.

Sahuagin 3 attempts to come after Stanley since he was just attacked by him: 

• Attack: 16 Damage: 4 piercing damage
• Attack: 11 Damage: 5 slashing damage
• Stanley takes 2 piercing damage

Sahuagin 4 swims forward to attack Usul with a multi-attack:

• Attack: 15 Damage: 4 piercing damage
• Attack: 8 Damage: 5 slashing damage
• Usul takes 4 piercing damage

monster]Sahuagin;Sahuagin 5[/monster] swims forward to attack Nalos with a multi-attack:

• Attack: 5 Damage: 5 piercing damage
• Attack: 16 Damage: 2 slashing damage
• Both attacks miss

((I noticed that as I edited this thread, likely because I altered the rolls against Snurk, the rest of the rolls kept re-rolling every time. So, ignore the rolls and just work with the adjudication undearneath them. If I said that they hit, then they did and if I said they didn't, then the original rolls didn't hit. Sorry for the confusion. I do try to minimize screwing that up, but in this case, I felt like it was warranted.))

Nalos is next.

Updated Map - Round 5, Turn 11 - Beginning of Nalos's Turn

(I forgot to move S3 over to Stanley, so the only correction to this map is that S3 is right in front of Stanley.)

Nalos uses his Bonus Action to try and attack Selachai:

• Attack: 12 Damage: 4
• The attack misses

Then, he casts Infestation at S5. The water swirls around and a cloud of sand flea-looking mites materialize forcing S5 to make a DC13 CON saving throw: 8. He takes 6 poison damage as the mites cover his body, biting him, and forces him to move 5' in a random direction (4 - South). This movement doesn’t provoke opportunity attacks.

It is now Usul's turn.

Updated Map - Round 6, Turn 1 - Beginning of Usul's Turn

((these guys have a big swim speed!))

Usul kicks back in the water, finding himself surprisingly comfortable to move while breathing in his helmet, swims back 10 feet, readies a bolt, and lets loose at #4

Usul successfully disengages, but misses his shot.

Darla is next.

Updated Map - Round 6, Turn 2 - Beginning of Darla's Turn

Darla will call out to the Sahuagin currently menacing Stanley, yelling "Stay away from 'im ye howlin dobber!", and casts Vicious Mockery at them(DC12 WIS Save, Damage:2 ), she'll then swim back to Usul's left side.

Sahuagin 3 DC12 WIS save: 15

The creature doesn't even really notice that Darla's over there talking crap to him. 

Snurk is next! (No map update needed.)

Snurk attempts to stab and kick the Sahuagin 

Attack: 17 Damage: 11 DC 12 Con 5 
Attack: 10 Damage: 7 

Having sustained Witch Bolt on S3, Stanley does more lightning damage.  10 

Quote from nschrock >>

Snurk attempts to stab and kick the Sahuagin 

Attack: 23 Damage: 4 DC 12 Con 5 
Attack: 21 Damage: 7 

Both of Snurk's attacks hit! 

Sahuagin 1 DC12 CON save: 20 - S1 is not poisoned.

Quote from Dipstick10 >>

Having sustained Witch Bolt on S3, Stanley does more lightning damage.  3 

Perfect. The damage is recorded. S3 is still looking pretty healthy, although you are definitely chipping away at his health.

The enemies are all next.

Selachai moves mostly South and a little towards Nalos and then attacks him with an eldritch blast:

• Attack: 20 Damage: 5 
• Her blast misses him, whizzing by his head

Sahuagin 1 attacks Snurk with a multi-attack  (one bite and one slash with claws):

• Attack: 9 Damage: 2 slashing
• Attack: 16 Damage: 4 piercing 
• Both attacks miss

Sahuagin 2 also attacks Snurk with a multi-attack:

• Attack: 6 Damage: 4 slashing
• Attack: 20 Damage: 5 piercing 
• Both of these attacks also miss

Sahuagin 3 attacks Stanley with a multi-attack:

• Attack: 14 Damage: 4 slashing
• Attack: 19 Damage: 5 piercing 
• Stanley takes 2 slashing damage

Sahuagin 4 attacks Nalos with a multi-attack:

• Attack: 20 Damage: 2 slashing
• Attack: 12 Damage: 4 piercing 
• Both attacks miss

Sahuagin 5 also attacks Nalos with a multi-attack:

• Attack: 6 Damage: 5 slashing
• Attack: 4 Damage: 3 piercing 
• Nalos is knocked unconscious! (But stable)

It would be Nalos's turn, but he's out. So, it goes to Usul next!

Updated Map - Round 7, Turn 1 - Beginning of Usul's Turn

All of the enemies still look pretty strong. S1 is the most hurt looking. He's, more or less, half-way dead. S2 and S4 haven't taken any damage, yet.

Usul will reload, try to calm himself in the water, and shoot at 5.

Unfortunately, Usul misses his shot. His bolt flying wide through the water and dropping into the trench. 

Darla is next. (The map didn't change with Usul's turn.)

((Don't forget that a couple of you have Inspiration. Feel free to use it. You obviously don't have to, though.))

 Seeing Nalos get knocked Unconcious, Darla curses, swimming backward(West/Left) as far as she can, yelling out at Selachai as she does, "Oi, ye daft ****, canny ye nae just **** aff!?" (vicious mockery DC12 WIS Save, Damage:1 )