Raker quietly moves back to Relic, saying in a whisper, “Six or so, sounds of kobolds and scraping, to the north at this junction.   Then other sounds, farther in and to the south.  We are in for something, I think.  Which way do you want to go?”  Raker pulls out his short bow and nocks an arrow, readying himself.  

As Raker rejoins the group, a kobold equipped with chainmail and a longsword appears at the edge of the darkness.

Initiative Order (will get filled in more when other enemies get revealed) //if I got your initiative modifier wrong in the campaign log, please let me know

21, Raker <--------------- current
[hidden combatant(s)] //noting this so MisterWhisker knows there'll be a small pause before Relic's turn; am not noting location of every hidden combatant(s)
17, Relic
12, Longsword Kobold
4, Gaius

Edit: As a reminder, squres with brown shade (I know the shading fro the light is making that a little tougher to see so please let me know if that needs adjustment on the color or if it's okay as-is) are rough terrain.

Hidden in the shadows, Raker draws his nocked arrow and aims at the approaching kobold.  After his shot, he moves with difficulty behind Relic and with a cunning action, he tries to hide again, using the warforged’s body as cover, but he can’t.  “Here they come…” he hisses.  

Short bow (with adv due to hidden) : 21 to hit, for 7 points of piercing damage, and 5 points of sneak attack damage.  

Movement : 10 feet to the west, over difficult terrain and squeezing past Relic.  

Stealth to bonus action hide : 13

The arrow flies from Raker's shortbow and lands a blow between the rings of the kobold's chain mail. A solid hit, but the kobold still has fight in it as it bears the blow.

Following that a ray of cold light appears from the darkness, momentarily revealing a robed kobold before it's shrouded once more. It appears to be aimed at Relic but misses the warforged.

Robed Kobold: Ray of Frost
To-Hit: max(20,9) = 20 (advantage for being unseen, though location is now known)
Relic's AC is 23 so a miss (base 21 + 2 from half-cover due to interposing creature)

The party is also able to hear the sound of running feet coming from the South.

21, Raker
20, Robed Kobold
17, Relic <--------------- current
12, Longsword Kobold (7 damage)
4, Gaius

Relic, realizing that he won't be able to reach the Kobolds quickly, decides to cast a spell. He moves forwards two squares to get a bit closer and casts [Tooltip Not Found] at the longsword kobold

Attack: 16 Damage: 2

Quote from Mister_Whisker >>

Relic, realizing that he won't be able to reach the Kobolds quickly, decides to cast a spell. He moves forwards two squares to get a bit closer and casts [Tooltip Not Found] at the longsword kobold

Attack: 16 Damage: 2

 (whoops... I'm not going to mess with the post just so that it doesn't change the roll, but Relic is casting fire bolt)

The firebolt strikes the longsword-wielding kobold for another blow. Furthermore, as he advances another kobold is unveiled in the dark.

 From the Northern branch another kobold, bearing a scimitar, dashes next to Relic. 

The kobold bearing a longsword mutters in Draconic as he advances. "This one tough, boys. Beware that axe." His approach is careful and measured. (Dodge)

As the longsword kobold advances another scimitar-bearing kobold passes him by and dashes towards the warforged.

Another kobold bearing a sling and dagger can be seen approaching from the North.

 21, Raker
20, Robed Kobold
17, Relic
16, Scimitar Kobold 1
12, Longsword Kobold (9 damage)
9, Scimitar Kobold 2
6, Kobold 1
4, Gaius <--------------- current
[hidden combatant(s)] //so a pause before Raker again

Gaius is a bit freaked out about all of the suddenly appearing enemies and for Relic’s well-being.   “Time for the thunder,” he mutters before casting Shatter just in front of the long sword wielding kobold.   He hopes to capture both facing Relic and the long sword wielded without affecting Relic.

Thunder damage = 16

CON save DC 14 for half.

[[OOC: Shatter has a 10ft radius which means casting it centered on the square in front of the longsword kobold would include Relic in the area of effect. So, in line with your stated intent, I'm shifting it 5ft to the right centered on the same square as the longsword kobold.]]

A boom resounds through the tunnels as Gaius casts his spell. The two kobolds are slain on the spot as the reverberations send them to the ground. The kobold bearing a longsword looks very wounded but seems to have avoided the full brunt of the thunderous blast. "Spread out!" he barks in draconic.

From the darkness two rocks come hurtling through.
Rock 1 to-Hit: 21 (adv from hidden, disadv from long distance)
Rock 2 to-Hit: 19 (adv from hidden, disadv from long distance)

With +2 from half cover due to other creatures, both miss Relic. 
[[OOC: Not revealing exact location of these ones in this case like the Robed Kobold on account of them being farther back in the darkness. But rocks are from Due East. (Right)]]

21, Raker <--------------- current
20, Robed Kobold
17, Relic
12, Longsword Kobold (17 damage) dodge
6, Kobold 1
4, Gaius
[hidden combatants]

Raker takes a Steady Aim to hone in on the scimitar kobold directly to the east of Relic, and lets loose an arrow.  “Looks like the whole lot is coming after us…”

Short bow (adv due to Steady Aim) : 19 to hit, for 5 points of piercing damage.  

Sneak attack damage : 9 points of damage.

Movement : 0

[[OOC: The XX label is meant to indicate they're dead. (I should've mentioned that in the last post. Sorry.) Both scimitars in front of Relic failed their con-saves and took the full brunt of Shatter damage. Was thinking I still wanted the tokens present on the map for bookkeeping.]]

((In that case, the target would be the next visible opponent, which would be the longsword kobold.  That would negate the sneak attack damage, but that would still be his target.))

[[OOC: Sounds good. With advantage form steady aim and disadvantage from dodge that would be a normal roll. So that would take the base 3 for a to-hit of 9. (From what I've seen, I think it's always the left one that's the first roll.) Correct?]]

As Raker shoots his bow his aim is true but unfortunately the arrow is deflected by the kobold's chain mail.

More running sounds can be heard from the South as another kobold bearing a scimitar appears.

To the East the robed kobold retreats back into the darkness before letting off another Ray of Frost at Relic.
Ray of Frost
To-Hit: max(10,17) is a miss //adv from unseen in darkness

21, Raker
20, Scimitar Kobold 3
20, Robed Kobold
17, Relic <--------------- current
12, Longsword Kobold (17 damage) dodge
6, Kobold 1
4, Gaius
[hidden combatants]

Since Scimitar Kobold 3 is still alive and not in full defense mode, Relic will attack it with his battleaxe

Attack: 20 Damage: 9

He will also cast booming blade, so if the kobold attempts to retreat it will take an extra 5 thunder damage

As Relic moves forward to attack the Scimitar Kobold another robed kobold is revealed in the Northern Tunnel and lets loose (reaction: readied action) a Ray of Frost at the warforged.
To-hit: 13, miss

Relic's attack the scimitar-bearing kobold is a hit! The slashes into it and leaves a grievous wound as the kobold barely stands.

The longsword kobold, seeing his best shot for an opening, moves forward for the attack to the square directly North of Relic and makes two attacks with his longsword.

Attack 1
To-Hit: max(13,13) //advantage from pack tactics

Attack 2
To-Hit: max(18,12) miss

In the wake of both of his attack faltering against the warforged's armor he orders, "Focus on the others!"

From the East a skeletal bird akin to a chicken comes charging out of the darkness.

In the Northern tunnel, Kobold 1 moves down and through the Longsword kobold's space to get into the Eastern tunnel with a shot on the other two party members. With Relic's immediate presence he's distracted but lets loose a stone from his sling at Raker.

To-Hit: min(19,15) miss

[[note: I'd say that attacking across a corner would be 3/4 cover for +5AC]]

ADDTIONAL note: the red line in the red tunnel is the limit of visibility (following that 5ft in around a corner is same light level, further is one light level lower)

21, Raker
20, Scimitar Kobold 3 (8 damage)
20, Robed Kobold
17, Relic
12, Longsword Kobold (17 damage)
8, Undead Bird
6, Kobold 1
4, Gaius <--------------- current
1, Robed Kobold 2

Gaius sees that this has gotten sideways really quickly.  Seeing the leader flank Relic spurs him into action.  He uses Distant Spell to cast Shocking Grasp at range against the longsword wielding kobold (at Advantage due to metal armor, 1 sorcery point used).

Ranged attack roll = 23, 24

Electric damage = 3

He takes a look behind them as well to see if he can see anything coming if he can.  (Passive WIS = 14)

Gaius' Shocking Grasp strikes the kobold and delivers a lightning jolt.

From the dark two rocks come hurtling at Raker. (normal rolls; disadvantage from distance; advantage from unseen attacker)

Rock 1
To-Hit: 9
Rock 2
To-Hit: 12

The Robed kobold in to the North advances slightly through the muddy ground and uses mold earth to create a rough earthwork to shield the longsword kobold from attacks from the West. (half cover, +2 AC when attacked from right/West) [represented by the brown line on the square's edge, counts as rough terrain if crossing over the edge-barrier]

21, Raker <--------------- current
20, Scimitar Kobold 3 (8 damage)
20, Robed Kobold
17, Relic
12, Longsword Kobold (20 damage, no reactions, +2 AC with attacks from right/West)
8, Undead Bird
6, Kobold 1
4, Gaius
1, Robed Kobold 2

Raker doesn’t like the way this is going, that Relic is getting surrounded.  He moves forward 10 feet, dropping his short bow against the wall as he goes and he pulls out his two short swords, wading into battle.  He walks forward another five feet and sees the pile of earth up against the longsword kobold, but he swings at him anyway.  

Short sword right hand : 25 to hit, for 10 points piercing damage and 6 points of sneak attack damage.  

If the longsword kobold stays up, he swings at him again.  If he goes down, he steps over the ledge and into his position in the middle of the 4 way corridor and swings at the kobold to the east. 

Short sword left hand : 9 to hit (suspect a miss)

Raker looks to the north quickly and sees the robed kobold, he also looks north and east for whoever has been slinging stones at them. He says to the south, “I’m behind you Relic.  Let’s smash these bloody kobolds to bits!”

As Raker charges the longsword kobold stands no chance from the blade of the shortsword and is cut down. Seeing his comrade fall Scimitar Kobold 3 calls out, "Retreat!" As Raker brings down the second blade the next kobold in line dodges out the way. 

The scimitar kobold, sheathed in booming energy, stands in the face of relic with fear in his eyes and tries to land a hit.
To-Hit: max(13,14) //miss

The Robed Kobold lets off another Ray of Frost at Raker and then heads further into the Eastwards darkness.
To-Hit: max(21,16) //21 > 18 [base 16 + 2 from half-cover from other creatures] so a hit
Damage: 8 cold, movement reduced by 10ft

@Gaius: Forgot about it in the last post, but with his look to the back Gaius is not able to spot anymore advancing kobolds or other enemies.

21, Raker (8 damage, movement reduced by 10ft)
20, Scimitar Kobold 3 (8 damage)
20, Robed Kobold
17, Relic <--------------- current
8, Undead Bird
6, Kobold 1
4, Gaius
1, Robed Kobold 2

Relic will go ahead and attack the Scimitar Kobold, with booming blade

Attack: 24 Damage: 5 plus 4 thunder damage if it attempts to move