[Now I shall use the Wiki for the bosses until the moonlit black cat ark starts as the anime didn't show a lot of the early bosses]
Mint and the copies leave but not before Asuna chased after the demon emperor and asked "Hey! weren't you paid to support me or something, where are you going!", the copy simply said "If I was paid to do so, I would have tried to deny that statement from the start, but in reality that assumption was wrong and I'm in his guild anyways." at the end of the sentence he points to Mint that is waiting for them to finish chatting patiently, Asuna slightly pales at that moment because he was right and she distanced him from herself for no reason. When the copy was sure Asuna won't say anything he started walking away and continued walking to the next floor with the others. Kirito wanted to follow Mint but he received a message that said "Continue training and find friends you can trust." with it he received various information on hunting grounds and good quests on the next floors.
When they enter the open second-floor Mint opens wide his arms and 5 kinds of wings sprout from his back, one pair are bat-like wings [like the ones Orcus has], another pair are scaly large wings he can wrap himself with that are wreathed in flame [pit fiend], another pair are large black feathered wings, another was a pair of large, leathery wings colored black but with a silver trim, and the last pair was what seemed to be spectral blood-red Roc wings. When Mint unruffled his wings and spread them out he said "Massacre the monsters and use familiars to tell the battle-ready copies to go", the copy replied "Of course, it's a relief to be free from that unreasonable girl... now time to massacre them!", the copy released 4 demonic wings [they have several pairs of wings according to rank, God- 5, Emperor-4, King-3, and duke-2] and flew toward a certain direction, and the demon kings flew as pairs toward other locations, when it was Mint's time to fly with a single flap he traveled a kilometer easily and arrived at the City Urbus, booked the best inn and started waiting until the next boss meeting will start, but he didn't just sit and wait, he started crafting a good scythe for himself and used fiends to hunt in the perfect grounds, specifically bearded devils [CR of 3] {Barbazus or Bearded devils were 6 ft (1.8 m) tall, often green-skinned humanoids, with muscled bodies. Their signature feature was their disgusting, wiry beards, which were occasionally infested with white maggots, although they could also be recognized by their pointed ears and long tails. Their skin was moist but covered in scales, and despite having clawed hands and feet they almost always carried massive saw-toothed glaives} and nightmares [CR of 3] {Nightmares were evil creatures that appeared to be large black horses with flames wreathing their hooves, flowing forth in the shape of their mane and tail, and trailing from their nostrils and red eyes.}, as they are both CR of 3 they could be summoned together by Mint, Mint is close to leveling up to level 20 so he won't try too hard for now.
Like in the progressive novel Kirito and Asuna team up and stuff and fix issues... as there is a 12-day gap between the opening of the second floor and the defeat of the boss Mint went out and slaughtered a bunch of mobs from boredom, as 1 day is left Mint leaves the shaking mobs behind him and goes on, but before that he snaps his finger and the area resets to what it was before, Mint is around level 26 now, the emperors around 22, the kings around 19 and the dukes around 17. he gathers the copies of all demon kings and the demon emperor of demons and the chaotic fiends emperor's 8 hell hounds [CR of 3] {Hell hounds appear to be canines with emaciated features, fire spouting from their red glowing eyes, and smoke pouring from their fanged mouths. The average hell hound stood 4.5 feet (1.4 meters)} that appeared by him using his ability
The demon emperor will go kill Nato the Colonel Taurus with the 4 bearded devils and 6 hellhounds, while Mint will go kill Baran the General Taurus with the 4 demon kings, 6 hell hounds and himself. We will see the demon's emperor fight first.
You could see a white-haired, emotionless, handsome young man riding on a fiendish horse toward a bull-headed beast with 4 devils with wiry beards riding the same kind of horse, and near them, demonic hounds around towards the same target, as the bull-headed beast noticed them it was too late as the young man threw his spiked flail at his horns and at the same time raised his hands and said "I summon thee, Babaus!" as he finishes speaking 2 portals appear and from them come running Babaus wielding 2 spears [CR of 4] {Babaus stood about 6-7 feet (2.1 meters) tall, their height accentuated by their elongated form. Their bodies were so gaunt that they appeared skeletal, covered in a form-fitting, black, leathery skin. Contrasting their emaciated forms were their oversized extremities, as their hands, feet, and head were more appropriately scaled for a hill giant. Like the rest of them, their skulls were tall and long, with pointed ears and jaws filled with so many jagged teeth that they took up half its head. Jutting out from the back of their skulls was a single, long horn-like growth that curved forward and downward.} when they appeared the man mumbled to himself "I better finish this quickly or he'll kill the final boss without me..." also while he said this he attacked again with the flail and accurately hit the horns again staggering it, the devils that ridden the horse reached the monster and hit it with glaives that caused infernal wounds and while the horse passed the monster the beards on the devils pierced it causing the beard to poison the monster, when the Babaus were close enough they threw the spears towards its face and neck, after they threw the spear they brandished their sharp talons and struck its belly while running and after that they retreated, now the young man said "Fire your breaths of hell!" to the hell hounds in a formation and prepared to fire, suddenly breathed a firey burst from their mouths that burned the monster, after all these barrages the monster's last health bar is in the red, with only a silver of health left, the young man then heard a roar that is more powerful than this monster's, and when he heard it he smirked and said "just in time" while he threw the flail to finish off Colonel Nato.
[Simplified fight with stats: Nato has 100 [a guess] hp each bar so 300, demon Emperor stunned the Nato by hitting its horns with a flail causing {13 damage}, then the 4 bearded devils used their Glaives {32 damage} and beard attacks {24 damage plus the poison condition from the beards [the poison didn't really do much but yep]}, the glaives caused infernal wounds that made the Nato bleed {20 damage}, and again Nato is stunned by another flail from the demon emperor {13 damage}, both Babaus threw the spears{28 damage}, then they stabbed Nato with their claws twice {32 damage} and retreated, the fire of the breath of the hellhounds fried Nato {126 damage}, only 12 health remained for Nato and he got finished off by the demon emperor.]