Vivi's eyebrows furl as she looks at the red lantern. She doesn't understand what it means, but red is usually a bad color in her experience. "Oh. It's red."

Luthok looks about him, but doesn't see any signs of undead inside the library. However, he starts to hear a commotion outside...

Where Dyoken stands, he sees people running past the shop window. The old elf man starts to waddle over to the door, "What could all this be about?"

Muireach will look outside.

(Shhh. This is a library...)

 "Thank you very much" Dyoken shakes the man's hand gently before he leaves (Athletics w/disadv.: 11.) He's really learned a lot about practiced restraint.

He turns and looks around for the gog before he heads toward the library to meet up with the others.

He stops in his tracks at the commotion outside. (Perception: 17)

Anyone looking or standing outside will witness a similar scene - mayhem and chaos!

You see people fleeing toward the marketplace from down the road and hear a bit of fighting in the distance. Muireach can't see what the people are running from, but he might have a good guess.

Dyoken, on the other hand, sees what he can only describe as a horde of undead attacking guards down the street from him.

(Dyoken is brown dot. Muireach, Luthok, Merrick, and Vivi located at purple dot. Red dot = the zombies Dyoken can see. Arrow represents the flow of people running.)

“Well... I guess this is happening again. Luthok, we have undead around. I think they’re coming from that way.” Muireach points down the road. “We should probably do something, I suppose.”

"THIS IS WHY I DON'T GO INTO TOWN!" Luthok gets up and gestures for Vivi to follow him and starts jogging with a limp towards the commotion. "GET OUT OF THE WAY!" He rips off his mask as he exits the library and makes his way through the running crowd.

Muireach follows!

"Looks like its about time for you to pay a visit to your son as well..." Dyoken steps out into the stream of people. He probably can't stop an undead horde though. As he stands to face the foes he also falls back toward the library.

He moves back slowly ready to finish anything that gets past the guards.

Merrick definitely hears all this hubbub going on outside as Ashe stops leading him to the room and casts a concerned look near a window. They reached the upstairs by this point. He sees his allies running outside through said window. (He can make it to the obviously incoming battle w/o any penalty to his turn.)

Luthok, Muireach, and Vivi reach the opening of the street that seems to have the most commotion. They spot the hoard of zombies and skeletons being held back, barely, by the local guards. Within seconds of their arrival on the opposite end of the street, the wall of guards finally breaks, allowing several ranks of the undead to escape and make it close to where Dyoken stands as he is about to head back to the library. The undead seem distracted by the few innocent people who still haven't made it to the marketplace just yet. 

Dyoken and Muireach both spot a small, horned, white dog panting heavily near the closest zombie. It yips and growls at the zombie between happy glances at Dyoken. When spotted by you, it yelps and runs further into the alley.

Combat Begins!

Turns:
Merrick 
Muireach 
Vivi
Skeletons
Dyoken 
Bystanders
Luthok 
Zombies

When you take your first turn, please roll perception at disadvantage! 

Map

Luthok will dash up towards the undead horde in front of him, grasping the lantern on his back with one hand and staff with the other. The staff glows sickly green once more. 

Action: Dash
Bonus action: Cast Shillelagh 

Movement: Getting close to the shop where Dyoken started.

Perception: 10

Muireach will trudging toward the undead horde. As he reaches the end of his movement, he vanishes from sight, reappearing in the middle of the undead. As he re-enters the material plane, light seems to dim and fade, like a candle in a heavy wind. The air grows frigid as frost begins to collect along the surfaces of objects. “Winter comes for you. Death hunts you like a rabid beast. Run. Hide. Cower. The cold will choke the life from you. The wind will steal your voice. Wolves will gnaw on your bones. Let those that hear the rumbling storm tremble and... despair...”

Winter Fey Step! Skeleton at the back must make a DC 14 Wisdom Save or be Frightened of Muireach for 1 Minute

Meanwhile, Muireach swings a Green-Flame Blade towards the Zombie at the back, Attack: 16 Damage: 12 magic slashing and 4 Fire Damage to the Zombie next to him.

Perception: 9

Merrick fires his bow, then runs to take cover at the building behind Dyoken.

To Hit: 2d20kh1 (15, ) + 6 = 21 Damage: 1d6 (4) + 4 [Piercing] + 2d6 (3, 3) = 14

DK sees the threats break through, he draws his whip and his nostrils flare with rage. He moves a few feet to his right and cracks his whip at the Zombie that's moving on the weird gog, hitting 24 with Reckless advantage for 9 slashing.

He shouts at the monsters as he steps back another 10 feet. "Now you're in trouble! You shoulda stayed dead!" 

(Perception w/da: 16 [Auto-corrected da to ad that's a 10 with da.])

Merrick shoots at nearest skeleton (1). The arrow just barely hits the skeleton (1), but Merrick isn't able to tell what damage he did to the thing as the skeleton (1) still stands. He manages to make it into cover behind the building.

Muireach attempts to scare the skeleton (2) in the back! (Skeleton's Saving Throw: 6) The chill air around Muireach quickly dissipates as he ignites the sword with flames and slashes the zombie (1) in the back with a side slash. The flames jump from the blade to the other zombie (2). They both groan in anger at the attack.

Vivi will run straight toward the hoard of undead and summon her scythe with a flourish. She disappears briefly before reappearing behind the southeastern most zombie(3). She makes a scythe attack! (Attack: 21 Damage: 13 slashing.)

Suddenly, two yellow arrow-like beams fly at Vivi! (First Attack: 10 Damage: 11 Second Attack: 7 Damage: 6 , both Force.) They seem to have come from above.

The skeleton (1) that Merrick shot lifts its bow but seems to lose vision of the halfling. Instead, he takes aim and shoots Dyoken instead! (Attack: 11 Damage: 3 piercing.)

Skeleton (2) runs back toward the direction it came from!

Dyoken easily lashes his whip and causes massive damage to the zombie (3). He sees puss spill out from it's back. The dog he is trying to attack yips with glee as zombie (3) slumps to the ground.

The bystander near the skeleton (2) in the back attempts to run away! Skeleton (2) attacks them. (Attack: 7 Damage: 7 piercing) The other bystander seems too scared to move...

Luthok arrives and notices a dog with strange horns yipping at a damaged zombie (3).

Zombie (1) and zombie (2) attempt to slam into Muireach! (First Attack: 13 Damage: 6, Second Attack: 19 Damage:  4 bludgeoning.)

Zombie (3) near the dog will turn to face Dyoken. It shambles toward him and attempts to push the strong man with its hands. (Attack: 16 Damage:  6 bludgeoning.)

Zombie (4) (who is nearest to where Dyoken started) spots Luthok run up. It groans as it approaches and tries to slug the dwarf. (Attack: 14 Damage:  6 bludgeoning.)

In summary:

 ??? has entered the round and moves after Vivi. None of you have spotted them. Now that you know they exist, you may make a Perception Check (without disadvantage) at the end of your turn to locate ???.

Muireach, flourishing his blade and leveling it as Zombie2’s throat, “I never like this season. I feel the compulsive need to reflect on my life and write poetry. I wonder what will kill you first, my blade or my prose.”

Muireach swings for the second zombie’s head with a green-flame blade, Attack: 15 Damage: 10 magic slashing damage + 4 fire damage to Zombie 1

Merrick runs out of cover, making a slash past the first skeleton. The rapier goes right underneath the skeleton's ribcage, and Merrick makes a deft twist of the handle. The rapier's turn causes the skeleton to explode into small pieces of bone. The halfling then ducks behind Dyoken, hiding behind the large man. He then takes a moment to scan for the attacker (Perception 8)

Move: Run out of cover, attack S1, then hide behind Dyoken
Bonus: Hide  21 
Attack: 26 Damage: 30

DK attempts to deflect the arrow from the Skeleton, reducing the damage by 2. (Assuming my discord roll is what the skele uses reducing from 3 damage)

"You can't go striking my friend now. Can't you see I'm an easier target?" Dyoken Recklessly punches the Zombie(4) gnawing on Luthok, and tries to drag it off, hitting 15 for 8 bludgeoning and grabbing against 19 skill, before pulling the Zombie(4) ten feet up the road toward the fray and holding the creature and its snapping teeth in front of himself as an inhuman shield. (To gain half cover if possible.)

"Get 'em Gog!" DK shouts to the horned animal.

(Perception: 16)

Luthok runs up towards the middle of the undead horde and tries to get as many of them in the aura of his lantern. A cloud of spores erupt from his beard onto one of the nearby zombies before he shouts "When an old dwarf has to save ye, you should get your lives together" he shouts at the nearby peasants as he activates [Tooltip Not Found].

Movement: As close as possible without triggering AoO
Bonus Action: Halo of Spores, 3 poison dmg at nearest zombie 
Action: Use Lysuna's lantern to cast Turn Undead Radius: 30 feet Wisdom save 12. If the creature fails its saving throw, it is turned for 1 minute or until it takes any damage.A turned creature must spend its turns trying to move as far away from the lantern as it can, and it can’t willingly move to a space within 30 feet of the lantern. It also can’t take reactions. For its action, it can use only the Dash action or try to escape from an effect that prevents it from moving. If there’s nowhere to move, the creature can use the Dodge action.