Barnacle's Reaction:

Motes of light form in the water and then begin to crackle and spark. Watching on as Shaolar completes the arcane motions, he sees the mage's outstretched finger clearly point towards Shanty as energy arcs out...

Closing his eyes, Barnacle hopes Shanty is able to weather the storm, some of his new companions aren't as durable as he is.

Suddenly wracked with pain in his chest, then across his body, Barnacle opens his eyes, finding himself shielding Shanty with his body.

(If it means Gulp is still a whale, then he is swimming straight to Gar and Shaolar, and attacks Gar)

Tail attack first: Attack: 16 Damage: Unable to parse dice roll.

Bite:  Attack: Unable to parse dice roll. Damage: 25  (DC 14 Dexterity saving throw or be swallowed)

(No OA on the fleeing undead)

Between the choices of falling inevitably from fleeing or falling heroically fighting to the end, Undertow grimly smiled as the one choice won out in the end. He'd come this far to help in the defense of sea and land, and he'd sooner go synchronized swimming with Sahaugin before giving the ideal his very best! Though following Bubbles demand, he clicks his tongue and still gets to stabbing at the least the one to thin the heard a bit more, before attempting to swim away closer to Amble, hopefully making her job easier.

Action: Shore Seeker Flurry at any injured Sailor(specifically injured by Bubbles. If none available, attack fresh one twice.)
#1 Strike - Attack: 11 Damage: 8 magical piercing.
#2 Strike - Attack: 13 Damage: 12 magical piercing.

Movement: AO-24(or as close as possible), risking OAs.

Bubbles' frustration is adding up. He tasks the others with finding Gar and swims around the pack of undead {AR-29} to make sure his next attack is aimed at the most undamaged-looking one. Two flings of Last Rites, one of which is accompanied by a burst of divine power, are enough to claim yet another kill. (Undead Sailor #11 takes 58 magical piercing and radiant damage and is DEFEATED.)

Without having to move, Bubbles thrust his weapon against another nearby sailor, but this one manages to withstand the blow. (Undead Sailor #12 takes 27 magical piercing damage.)

(OOC: I'll resolve Gulp's turn next once I get clarification on the question that is pending in the OOC Chat.)

OOC: Just a little retrospective narrative license

As Bubble pulls back from his last thrust, he looks around again trying to see  any movement that might give him a idea of Gar's location, and an idea forms as he reflects on the makeshift light attached to he weapon, and yells out "Can anyone use magic to light Gar up?"

DM's Screen:

(@MuggsHill: Nice piece of RPing there! You can have a DM's Inspiration token.)

(OOC: For Gulp's turn, I'm going by instructions shared in the OOC Chat.)

Whale-Gulp whirls in place as to strike one of the two remaining undead sailors with his tail. The sailor that just barely survived Bubbles' last attack is effectively pulverized. (Undead Sailor #12 takes 18 bludgeoning damage and is DEFEATED.)

Moving forward just a tad, Whale-Gulp then bites the last remaining sailor. The teeth hit the undead creature but only as a glancing blow, such that the whale fails to "gulp" it. (Undead Sailor #15 takes 17 piercing damage.)

-> Rusted Longsword vs. Whale-Gulp: Attack: 17 Damage: 5 

-> Whale-Gulp's CON saving throw {DC 12}: 20 

Whale-Gulp then follows Bubbles' suggestion and begins to swim in search of Gar, but not before taking a swipe from the surviving sailor. Just as he reaches his new spot (occupying the 4-square diagonal connecting {AC-23} to {AF-26}), the whale's echolocation picks up the presence of the enemy duo. (Whale-Gulp takes 5 slashing damage.)

@Gulp:

DM's Screen:

It is Shanty's turn to follow one of Bubbles' suggestions. Expecting Gar to reveal himself sooner rather than later, the bard readies a casting of the Light spell. Then, in the corner of his eye, Shanty catches a glimpse of the last undead sailor standing. He commands his Tentacle of the Deeps to attack it. It does so successfully, although it fails to put the creature down. (Undead Sailor #15 takes 5 cold damage and has its speed reduced by 10 feet.)

LEGENDARY ACTION

Gar torpedoes himself toward Shanty {AK-25}. The bard releases his spell, aiming for Gar's trident, but the enemy avoids the spell in the last second.

(@Blue: Whale-Gulp can perform an opportunity attack against Gar, but it has to be a tail attack due to range. If you do, roll a d20 to account for Mirror Image.)

(@Shadow: The ready action here was just so the attempted spell would make sense, as Shanty did not have a visual on Gar at the beginning of his turn. Since it all kind of happens almost at the same time, I'm willing to wave away the idea that readying a spell would disturb concentration this time around.)

DM's Screen:

Undertow grips Shoreseeker tightly and attacks the last undead sailor engaged with him. The first poke spills some of its putrid guts, the second puts it down. (Undead Sailor #15 takes 20 magical piercing damage and is DEFEATED.)

Thinking himself free of assailants for now, Undertow then begins to swim toward Amble's faint light. A moment after turning to start his move, the ranger sees what faintly resembles a face in the water.

-> Slam vs. Undertow: Attack: 17 Damage: 19 

Undertow avoids the malignant current and approaches Amble {AO-26}. 

LEGENDARY ACTION

Gar thrusts his sentient trident into Shanty:

-> Wave vs. Shanty: Attack: 31 Damage: 17 

-> Shanty's concentration check {DC 10}: 12

Shanty fights to keep concentration on his spell as the trident sinks into his flesh. (Shanty takes 11 magical piercing damage.)

Still smiling widely, Gar floats sideways briefly {AJ-25} and commands Wave to release one of its magical effects. "I still have plenty of tricks up my metaphorical sleeve!" Shanty and Barnacle both feel like something has changed in their immediate vicinity, though they can't be entirely sure what. (OOC: They both can attempt a separate arcana check to try to understand what happened.)

(Sandlot is up next. There is nobody within 10 feet of him so he only sees Bubbles and Amble due to them having their own sources of light. He can also make out Undertow's silhouette right next to the tortle.)

Frankly at a loss on what to do now with no sight on the enemy, let alone their location beyond the roughest approximations, Sandlot lets the fear and frustration free reign to roam within and without. Then, taking a deep breath(gulp?), his expression softens into a peaceful and resigned one. Seeing the state of of some in the gloom, the temptation to spare no expense in mending hurts or offer protection floats about in the back of the aged Locathah's mind.

But instead, he floats northward with half-lidded eyes, passively searching for something along the bodies on the ground. Eventually he seems to find a spot just clear enough to sit down among the dead. At which point the straps are undone on the shield, allowing it sink freely to the ground. And if the moment alloted for it, all other vestige of a weapon too would've been discarded as well. Yet without time being at his leisure, settling on the shield being enough, Sandlot held his holy symbol in both hands before him, and... begun to pray. "O' Lady Eldath.... Mother of Singing Waters... Harmony's kin and kith.... Speak with you, thine child would... The hour late... the gloom deep... But never so dim that the light of your love cannot reach..." He said gently. And on he would continue, seeming distracted in the prayer. But, never was the prayer for victory, or protection, or strength. Nor did he pray for forgiveness; be it for him, his fellows, or even Gar. His prayers were in thanks to Eldath for all the blessings given so far, and for enduring some old codfish dalliance.

He would pray as well  to reaffirm his faith in her remains unshaken. His trust in her love and cleansing tears reaching Gar, and helping him find the peace forgotten in his long journey.

Movement: To AH-31, effectively going prone.

Action: Doff shield.

Future Reaction: If Shanty would take damage, using Protective Bond to take the damage in his place.

Delighted to see the enemy, Gulp tryied to help Gar to propell a bit faster (with his tail)

Tail AoO: Attack: 20 Damage: 21  (Mirror dice: 4 )

(@Ori: That was also a great little piece of RP. You also get a DM's Inspiration token.)

Whale-Gulp tries to strike Gar as he passes by but the agile enemy twists away from the approaching tail.

Noticing a lull in the fighting, at least from his perspective, Sandlot makes his way toward the noises of conflict. While moving, he decides to take a moment to reach out to his deity. The cleric sets his shield on the sea floor, sits on it, and communes.

LEGENDARY ACTION

Gar attacks Shanty again:

-> Wave vs. Shanty: Attack: 26 Damage: 9 

-> Sandlot's concentration check {DC 10}: 9

Sandlot feels a sudden ping in his consciousness and, in a fraction of a second, teleports to Shanty's side to take the trident attack on his behalf (Sandlot leaves his doffed shield behind.) Gar seems surprised by the feat. He has seen another locathah perform the same defensive move a moment ago, but he looks more surprised now. (Sandlot takes 12 magical piercing damage.)

(Malignant Sea Current goes next.)

Does the arcana check cost an action?  If not: 8

(@Shadow: No, no action required. Unfortunately, with an 8, Shanty can't quite make sense of the effect he felt.)

Undertow reaches Amble but it would seem he has an unseen pursuer.

-> Slam vs. Undertow: Attack: 27 Damage: 25

-> Slam vs. Undertow: Attack: 14 Damage: 12

The next attacks prove to be too much to an injured Undertow. The ranger goes down and is now within an inch of his life. (Undertow takes 13 bludgeoning damage and 2 DEATH saving throw fails.)

(Barnacle is up next. For the first time in this fight, he can see almost everything with a 60-foot range. He can also roll an arcana check as mentioned previously, no action required.)

Barnacle's Arcana check: 9

Sensing his time is now, Barnacle pounces on Gar, thrusting out his trident, probing the man-crab's defences.

"Have at you!"

Attack 1: 22 Damage: 14

Attack 2: 17 Damage: 9

(Expending one superiority die to make an attack that hits Gar a trip attack. There's 1d8 to add to the damage of the hit, so 6. Gar needs to succeed on a DC16 strength saving throw out be knocked prone, assuming he's a large creature or smaller.)

Much like Shanty, Barnacle can't quite make sense of the magical effect he felt a moment ago.

Barnacle spots Gar and tries to move toward him but finds himself unable to close the gap. He moves around and tries to approach Gar from a different angle {AL-25}. Once again, Barnacle fails to get any closer than 10 feet from Gar, as if invisible walls were separating them.

(It is still Barnacle's turn. He still has an action and bonus action, but has used half of his movement trying to get closer to Gar and failing.)

Barnacle's eyes narrow as he runs into one of the tricks hidden up Gar's metaphorical sleeve. Rubbing his face from the impact, he exclaims, "Dou sly phox!"

Arcana 8

@Barnacle: You have heard of magic which is able to create impenetrable and invisible walls of pure force. Judging by the angles from which you tried to approach Gar, you surmise that this villain has created such a barrier in a cubic form with sides that are approximately 15 feet long. Gar is situated right at the center of this invisible cube, while both Shanty and Sandlot seem to be trapped in there with him.

(Shaolar will go next.)

Peeking at the battle from his ridding spot, Shaolar momentarily pokes out of his nook, sizes the opportunity to reduce the number of enemies in the battlefield, and then swims back behind cover.

-> Undertow's (unconscious) DEX saving throw vs. Acid Splash: auto-fails.

The already battered body of the ranger jerks one last time as a bubble of acid forces the last bit of life out of him. (Undertow suffers his 3rd DEATH saving throw fail and is DEAD.)

LEGENDARY ACTION

Gar snaps his claw at Sandlot, almost as an instinctive reaction to the cleric's sudden appearance next to him.

-> Claw vs. Sandlot: Attack: 17 Damage: Unable to parse dice roll. 

-> Sandlot's concentration check {DC 10}: 24 

-> The claw attack above was supposed to be rolled with advantage. Here's a second roll: 20

Sandlot's leg is caught in the large claws. (Sandlot takes 8 bludgeoning damage and is grappled.) 

(Amble goes next.)