Yes the skeletons are undead

Buppido: 16

Skeletons: 5

Sarith: 9

If you roll higher than either Buppido or skeletons, then go ahead with actions.

Sekkar activated Dawnbringer (that sent a happy war-call in his head - there were clear undead in a clearly sinister place) and run toward the closest skeleton - or two (he would not hesitate to attack Buppido himself, but that one was too far, lizardman hoped that the light would at least distract newborn necronacer)

Used skills:

 Attack: 15 Damage: 17 + 3

 Attack: 20 Damage: 11 + 8 + 4

On her turn, Rhayna will use her Channel Divinity: Turn Undead (DC14).

Initiative 19

Grabbing rope from her pack Kaylyn moves to tie Droki up.

Joetaro Initiative - 6

Joetaro is going to attack the closest skeleton.

Attack: 21 Damage: 10

Zeno will Bonus Action Dash past the skeletons, trying to skirt around them if he can with the extra movement (minimizing AoOs). He draws his colichemarde, stabbing at the Detroit, attempting to incapacitate him enough to stop whatever madness he is coordinating.

Attack: 9 Damage: 9

Battle in Buppido's lair

Joetaro hears the commotion, and at a nod from Kaylyn runs to help while Kastix assists with restraining Droki. Despite his furious wriggling to get free, they manage to hold him down and get a rope around his arms and legs.

Zeno attempts to weave his way through to Buppido, but the sheer volume of dead body parts on the ground makes the going slow, and he can't manage to close the distance. The mad derro in return lifts a loaded crossbow and fires it at Zeno, grazing his hip.

Rhayna calls on Selune's light, and three of the skeletons turn and flee. Two more press forward toward Rhayna, with one stabbing a rusty shortsword ineptly toward her. The other takes a bolt of radiant energy from Joetaro who has just rounded the corner enough to see the action, and a leaping stab from Sarith finishes the undead creature.

Sekkar's glowing sword sings with joy inside his mind as a single sweep of the shining blade both slices clean through one skeleton and elicits a cry of pain from Buppido, who is suddenly exposed to hated sunlight. A quick movement and a second swing at one of the fleeing skeletons likewise chops it down to the ground in one blow.

Buppido's shrill voice cries out: No, no this ain't right! Buppido must triumph! You will all fall before Buppido!

Zeno: Buppido is 50' away, and with difficult terrain and a circuitous route, Zeno wouldn't make it. I could substitute his attack for ranged, but would use the same attack roll (miss). Want to Dash instead? Something else?
Buppido's attack as it stands hits Zeno for 7 HP.

Joetaro: Also too far to close to melee, so I made it a spell attack. Still a hit, and an assist to a kill.

Kastix: I put him down as helping Kaylyn to restrain Droki.

Kaylyn: Make a DEX check to tie up Droki. Can add your proficiency (from Survival), and roll with advantage due to help from Kastix.

Only Buppido and one skeleton remain.

While still holding her pendant high, she yells “Halt!!” to Buppido. Rhayna casts Command (DC 14).

Kaylyn struggles with the squirmy Droki while Kastix lends a hand as she tries to secure the ropes.

Rope tying - 19

"Oh shut up! We'll just kill you like everyone else" Kastix shouts down the tunnel as he makes his way down the tunnel at a dash. 

Joetaro is going to make his way down the tunnel and use his full movement.

(Forgot about the difficult terrain. I’ll Dash again which should make it like 45 feet, still just out of melee.)

Zeno closes the gap, and slashes with his colichemarde

Attack: 14 Damage: 13

And offhand, bonus action with dagger:

Attack: 25 Damage: 2

If anyone else is engaged with Buppido, sneak attack, 6

Sekkar was thoroughly enjoying himself (as did Dawnbringer). "Hello" did not really went as planned but it looked like Buppido was taken care of. Lizardman went after the remaining skeleton:  Attack: 13 Damage: 16 + 7

Droki DEX check to escape: 6

Kaylyn barely has time to secure the knot before Kastix also scoots off to help, leaving the warlock with the struggling derro. In his wriggling his hat falls off and he yelps with alarm that it will no longer 'attack' anyone for him, but one he realises he can't escape the bonds, he again calms down, resorting to simply hissing at Kaylyn.

Picking his way quickly through the gruesome floor-coverings of random body parts, Zeno finally draws nigh to Buppido. With a single stab of his ancient sword, Zeno pays Buppido back for his crossbow bolt, with interest. A stab through the heart is enough to drop the derro, and as he slumps to the ground with a look of disbelief on his face, he cries out: Buppido cannot die... will rule you all... end of the world... Rhayna holds her pendant aloft, but it is too late. The eccentric derro, the former cellmate and comrade-in-chains, was no more.

Joetaro enters the cavern, with Kastix not far behind, just in time to see Sekkar's blade of light cut through the remaining skeleton like it was made of rice paper. As the bones fall to the floor, Joetaro hears a voice off to the left saying: Well, I'm glad he's gone! Looking in the direction of the voice, the paladin sees a spectral head, with the features of a gnome, poking up out of the ground.

Joetaro jumps at the site of the head. "Do you mind coming out of the ground? You could give someone a heart attack."

Oh! To be sure! says the ghost head, and as it rises in the air, the rest of the ghost body emerges fully from the ground. Beggin' your pardon, but I do be gettin' used to bein' down there, as that be where the rest o' me be layin'. Our man there chopped me up into pieces not a tenday ago, and spread me bits all around 'ere. Mighty glad I am that ye finished 'im off, 'e were a real rotter 'e were. Now I ain't seen folks like you 'round these parts before, what's the story?

Kaylyn gets a quizzical look on her face.  Did she understand that right?  She casts Detect Magic and she looks down at the bound Droki.  "What do you mean?  The hat won't attack anyone else?  Or someone/something else?  Speak Droki, tell me."

"Surprisingly this is not weirdest thing I've seen in this underdark," Kastix comments on the ghost head, seeing the battle is done already, "I better help drag our guest here," He turns back heads back to Kaylyn  and the Derro prisoner.

(Can Rhayna use Gentle Repose on the ghost?? :-)

Rhayna grabs Stool, so it won't have to wade through the corpses, and she keeps it in her arms. She gets closer to the ghost. "Please, we are not here to harm you. What is your name? My name is Rhayna, and this little guy here is Stool. Pleased to meet you."