"Well alrighty then, seems they are dangerous."

Initiative 21

A silvery beam of pale light suddenly shines down in a 5-foot-radius, 40-foot-high cylinder centered on the closest mephit to Zeg.  Dim light fills the cylinder.

When a creature enters the spell’s area for the first time on a turn or starts its turn there, it is engulfed in ghostly flames that cause searing pain, and it must make a Constitution saving throw. It takes 2d10 radiant damage on a failed save, or half as much damage on a successful one.

Attack/Save: CON 13 

Damage 9 radiant

Moonbeam

Initiative: Navi 22, Zeg 21, Flynn 17, Mephits 14, Faelan 13

@ixi: if you want to proceed with Radiance of the Dawn, then go ahead and roll the damage.
@someredshirt: an attack roll (or some other action) from Flynn

and then I'll proceed with any mephits remaining...

Flynn steps in front of Navi and the egg blade ready

(Assuming Flynn still speaks.gibberish)

Hold action till something gets.close

@someredshirt: There are three mephits directly beside Navi spitting mud at her. Did you want to attack or did you have some other trigger in mind?

Oh in that case Flynn attacks

Attack: 11 Damage: 6

I tried using the website's roller, but forgot how annoying it is. Can't change edit text after rolling or the rolls change. I'm just gonna use a different method (or real dice) and post my numbers in the spoiler. You can all do the same if you wish.

Navi's explosive sneeze lights up the marsh, turning it from perpetual dusk to high noon, as the dozen converging mephits gurgle in agony, their muddy skin drying, cracking and blistering in the bright light. Then to add insult to injury, just as the daylight fades, a beam of moonshine highlights three of the now-injured mephits and worsens the damage. Flynn gallantly puts himself in front of Navi and protectively stabs at one of the creatures, who gurgles in pain as the sword pierces its wing.

Now clearly agitated, the mephits move in, with the gurgles turning into heaves, which become great spews of mud from the mouth. Twelve gouts of mud splash over the group, threatening to glue them in place and leave them at the mercy of the filthy creatures...

Everyone must pass a certain number of separate DC 11 DEX saves or become restrained for 1 minute
Zeg and Faelan: Have three mephits on them each, so please roll three saves each
Flynn: Has three on him also but has also attracted the wrath of one of Navi's, so please make four rolls
Navi: One mephit has gone after Flynn, so please make just two rolls

Then everyone can please take their turns

Dex saves

1. 4

2. 22

3. 21

4. 3

(#2 is a nat 1)

I'll use the dice roller on the character sheet that gets posted to the campaign game log.

I rolled a 6, 10 & 5

Restrained as he was Zeg continues to keep the bright beam of light on the 3 Mephits.

Attack/Save: CON 13 

Damage 14 radiant (see game log)

Moonbeam

(Thank you for rolling her damage! Apologies for the delay. Busy bday weekend.)

They knew how to light up a room!

Not expecting to be spewed on, Navi practically doesn't even think to move until the last moment. Despite her natural speed, she's sprayed with mud. The little fairy blinks. Now, she didn't have another powerful sneeze in the tank, but she did know how to flash unwanted attention. Navi would flutter her wings. She'd start to strobe in radiant light, faster and faster. "Whoop!" She chimes, erupting in a small burst of radiant light.

(Dex ST: 7 and 9)
(Casting: Word of Radiance Con Save DC13 or take: 4 radiant damage)

(Sorry for the delay)

DEX Save: 21

DEX Save: 19

DEX Save: 11

Faelan dodges the first mud spew, but the second one hits him square on his chest. Now, he's stuck in his place.

(Questions: Are Mephit(s) in melee range to Faelan? For Dreadful Strike can it be used on only one creature per turn or more than one? If he switches to his longbow, that will be his turn right?)

(Dreadful Strikes - You can augment your weapon strikes with mind-scarring magic, drawn from the gloomy hollows of the Feywild. When you hit a creature with a weapon, you can deal an extra 1d4 psychic damage to the target, which can take this extra damage only once per turn.)

The sudden gouts of mud from the vile creatures are more than sufficient to glue everyone in place, making it difficult to move and impossible to fly. However it didn't prevent the two winged companions from having their moment to shine. Navi's strobe causes nine of the twelve mephits to gurgle in pain as the radiant light causes their muddy skin to dry and crack. And Zeg's powerful beam of moonlight is too much for two of those, and they crumble into dirt and drop into the swamp, with the third one barely holding itself together.

Mephits #4 and #5 are defeated, with #6 very nearly dead. All the other nine are injured to some degree.

@Faelan: Yes, the mephits can all be considered to be within melee range for the purpose of this combat. Yes, Dreadful Strike can be used on more than one creature, if you are hitting more than one creature with a weapon in the same turn (presumably with Two-Weapon fighting). And yes, equipping a Longbow would require an action, and you'd have to drop the two scimitars.

@ALL: Oh, and I forgot to mention, you can repeat the DEX saves at the end of your turn (just the failed ones). So I think three for Zeg and two for Navi, three for Flynn and just one for Faelan.

Even though Faelan is stuck, he strikes the Mephits in front of him.

Scimitar Attack1: 17 Damage: Unable to parse dice roll. (+1 psychic dmg)

Scimitar Attack2 (BA): 8 Damage: 8

(If the first strike is enough to finish the target, the second strike is on a new target and +2 psychic dmg)

Dex rolls are 10, 6 and 14

(Sorry, it's been a long time since I managed a combat on PbP, so I'm a bit rusty. But I have my trusty spreadsheet up and running now, so hopefully I'll get a grip on this.)

Also: Reminder that the restrained condition imposes disadvantage on attack rolls

Despite being caked in the foul-smelling marsh mud, Faelan manages to twist his furry wrist enough to swipe his scimitar through one of the mephits. A great blob of mud is carved out of one wing, and it falters in the air before refilling the void with more mud from its body, leaving it smaller and weaker but still animate.

-----------------------------------

Faelan: I took the liberty of making a disadvantage roll for the first attack, and it was 19, so still hits. I applied the damage to most-injured mephit, which is also that one that succeeded on mud-sticking Faelan, but all three are still alive. No need to reroll for second attack as it missed, but a reminder that you don't add your DEX bonus to the damage if using Two-Weapon Fighting. Please make one end-of-turn DEX save v Mud Breath (only one instance currently active)

Navi: still has two instances of Mud Breath causing the restrained condition, so please roll two end-of-turn DEX saves

Zeg: Although Zeg's spell destroyed two of the mephitis, their mud persists and continues to restrain Zeg. However the final DEX save passed, releasing Zeg from the remaining mephit's mud, so Zeg is now only restrained by two. No further rolls required yet.

Flynn: Second round action please, followed by three end-of-turn DEX saves.

(End of turn Dex Saves:)
(Save 1: 4 and Save 2: 13)

“Come at me!” The little fairy struggles to get her dukes up, maybe even slips but she’s feisty when meanies are picking on her friends. What poopy bullies! 

Faelan DEX Save: 6

(@DM In my Fighting Style it says the below. Unless I am reading it wrong.)

(Two-Weapon Fighting - When you engage in two-weapon fighting, you can add your ability modifier to the damage of the second attack.)

Flynn starts speaking lowly in a fierce whisper.staring at one of the mephits

Dissonant  whispers.  Wis 13 save or take 39 damage and move away from me on next turn----half damage on successful save

Dex saves.  12      2,  14    3.

 13