Of course neither Fran nor metallic Brutus did not care much about the stench but fiercely attacked the demon, "blooding" the thing. But before it could react, mad guards fully joined the fight. No, not fully - they did not try to cut anyone down, instead, with the mad hunger in their eyes, they tried to grab and bite anyone in the vicinity, apparently not even  noticing that they step into the stench cloud (save: 13 10) :

vs Choir: Attack: 11 Damage: 4

vs Choir: Attack: 6 Damage: 3

vs Adray: Attack: 20 Damage: 3

vs Unicorn: Attack: 21 Damage: 1

Polly!

     With the humans attacking, Polly has less concern with their safety.  She used her Bonus Action to direct the Gnombies to attack them.

G2 goes up and around U to the north to attack Human4 from the north.

G2 Attack: 16 Damage: 8

G1 and G5 also move up to Human4, but they’re attacking from a southerly position.

G1 Attack: 14 Damage: 8

G5 Attack: 9 Damage: 6

 G3 & G4 are moving into position to attack Human1 but I don’t believe their Zombie Shamble of 20’ gets them into position to attack this round. 
     OwImp is flying easterly.  Trying to get high enough to stay above the fight and extend his view, he’s basically still scouting for the demon that teleported away...

     Polly is flying southeasterly and muttering the mystic words to throw more Eldritch Blast at the demon...  shells aiming to be well south and maybe a bit behind it as well, wanting to avoid clumping and such.

Eldritch Blast 1 Attack: 13 Damage: 6

Eldritch Blast 2 Attack: 25 Damage: 9

Eldritch Blast 3 Attack: 16 Damage: 9

(Is Gust of Wind still going? 1 minute concentration spell.)

(It can, if Choir wish so, but if we are talking about stench - the demon carries stench with him, it can not be removed completely. For any other purpose - Choir is free to change the direction of the wind)

Zombie two limped all over the field to the guard attacking Mooncolor and ripped a big chunk of flesh from it's side (the mad guard is still standing but probably only by the magic of ichor).

Mean while Polly, unreachable by the demon, threw her force bolts at him. The demon retaliated attacking the one human in front of him, trying claw and bite the enemy:

Attack: 8 Damage: 20

Attack: 20 Damage: 9 (DA attack roll: 24)

Mooncolor, whose hide was covered with blood again from the bite of the mad human, softly flashed with the celestial light, that healed the wound: 11

Choir!

Then Fran, Brutus, Ordrag, Adray in Round 9

Choir is fixated on Demon S.  She moves forward. (If 5 hits her on an opportunity attack,  Wrath of the Storm does 9 thunder damage to it, DC 17 for half damage.)

Touching the demon, Choir makes a spell attack with Inflict Wounds at Level 6! Attack: 28 Damage: 45 necrotic damage.

Fran would return to using her crossbow and continue her focus on the demon. 

Attack 1: 25 Damage: 7
Attack 2: 10 Damage: 12 

Now able to attempt biting at it’s ankles, Brutus would chomp at the demon.

Brutus force empowered rend: Bonus action: 11 Damage: 9 

Huffing and puffing in his efforts to catch up with the fight, Ordrag jogs along in his heavy plate armor, finally joining the fray with not enough breath left to even manage a battle cry...

All attacks against big demon...

Action: Attack/Longsword.
Attack#1: 12 Damage: 9 slashing.
Attack#2: 20 Damage: 10 slashing.
Attack#3: 21 Damage: 13 slashing.

Bonus Action: TWF/Warhammer.
Attack: 10 Damage: 13 bludgeoning.

Reroll Longsword damage (first one if it's a hit, otherwise the second one. Use highest): 12

Adray focuses on the big guy with his attacks.  He does reign himself in a bit to keep his defenses up and damage to a minimum.  Adray lashes out with two quick strikes and then angles himself back to keep an eye on those trying to surround him.

Attack: 24 Damage: 10

Attack: 11 Damage: 10

bonus action: patient defense attacks against Adray are at disadvantage

Ordrag: a DC 14 Constitution saving throw or be poisoned until the start of your next turn.

Guard 5 was definitely trying to bite off a chunk of Choir with it's clumsy bite: Attack: 14 Damage: 2 (Save 14 ) but the determined kenku walked straight to the demon (Choir: a DC 14 Constitution saving throw or be poisoned until the start of your next turn) and touched it just briefly but result was devastating - demon's hide cracked open, making ichor pour out of the rotting wounds, shaping all over the massive body (that did not improve the odor in any way). Hard to say if demons are capable to feel pain, but that one roared.

Combined attack from every side visibly shook the monster, even forcing him to make a small step back and raise "hands" in defense rather than attack. But the mad guards did not stop:

4 vs Unicorn: Attack: 21 Damage: 1

1 vs Adray: Attack: 6 Damage: 4

2 vs Choir: Attack: 5 Damage: 2

3 vs Choir: Attack: 20 Damage: 2

4 vs Choir: Attack: 18 Damage: 2

Not one of them left as much as a scratch on anyone but the hunger in their eyes looked scary.

Polly!

     Gnight of the Living Gnombies Continues!  Gnombies 1, 2 and 5 all mindlessly slam themselves into Guard 4 as if acting under a single hive gmind...

Gnombie 1 Attack: 19 Damage: 7

Gnombie 2 Attack: 17 Damage: 10

Gnombie 5 Attack: 20 Damage: 8

     Gnombies 3 & 4 are still shambling easterly trying to catch up to the battle.

     OwImp is still flying invisibly around east of all this nonsense, scouting the area but also looking for the snakey demon that teleported away. Perception 18

     Polly is flying about two squares east and one north-east, taking a large swoop around the demon and eventually looking to be on the opposite side (but a good 20 or so feet away) than the rest of the party.  Best to have it surrounded and attacked on all sides.  Speaking of attacks, polly thrusts out her left hand and shouts "Boed i'r chwyth hwn eich taro'n farw!" and the pale, purple crackling energies squelch out towards the demon once more!

Eldritch Blast 1 Attack: 22 Damage: 14

Eldritch Blast 2 Attack: 18 Damage: 14

Eldritch Blast 3 Attack: 9 Damage: 5

(Choir CON save vs poson: 4) Choir gags and chokes in the foul stench.

While Choir was paying for her bravery, Polly, though half of her bolts missed the massive body, managed to simply finish the colossus - already decaying corpse practically melted on spot, leaving behind yet another deep puddle of ichor.

The gnoll-zombies in the same time lashed on guard number 4, annihilating him despite protesting neighing of Mooncolor. For a moment Polly felt conflicted, she new that Lulu was not here and yet felt as if hollyphant was hovering right in front of her, looking bot said and accusatory (Polly, a DC 15 Wisdom saving throw or get 1 level of exhaustion ).

Mooncolor jumped over the body of the dead guard and touched with it's horn guard 1 (previously attacking Adray). A flash of holy light - and the black goo covering guard melted away, the mad hunger in guards eyes disappeared and now sane (considering circumstances) human looked around in confusion.

Choir!

Then Fran, Brutus, Ordrag, Adray in Round 10

     Polly yelps in victory and raises a fist in victory! ((and takes 155 temp HP due to Dark One's Blessing...))

Wisdom save: 19

Choir, through her coughing, casts Word of Radiance. 2, 5 and possibly 3 must make a DC17 Con save or take 6 radiant damage!

"No, please! They do not understand what they are doing! Jay, Tal, Esselyn -- wake up, shake it off!" The pleading came too late (4 9 7  ), and though the radian light did not kill the mad humans, it certainly harmed them. Lulu's invisible presence (and disapproval of attacking the guards, mixed with the sadness) now was felt by Choir too ( Choir, a DC 15 Wisdom saving throw or get 1 level of exhaustion ). "They seemed to be cursed by this demon blood!" finally announced Mooncolor his verdict.

Quote from Kaemgen >>

     Polly yelps in victory and raises a fist in victory! ((and takes 155 temp HP due to Dark One's Blessing...))

Wisdom save: 19

 Obviously that should just be 15 temp HP

((I did feel something was wrong here :) ))

(Choir wisdom save: 22 ) (Oops, disadvantage for the poison, if that's still on: 18)

CON save: 12

(I couldn't help reading Kaemgen's post while pronouncing all the 'G's.)

Seeing the unicorn 'heal' one of the demonic guards, Ordrag stows his two weapons, runs over to another guard (#5 perhaps) and attempts to grab hold of its arms and prevent it from attacking anyone else until Mooncolor can restore it...

Athletics: 24

(Grapple replaces one of Ordrag's attacks. If we are able to deal non-lethal damage with unarmed strikes, then Ordrag will use his other two attacks against #1, kicking out with one leg to try to knock it down...)

Unarmed Strike #1: Attack: 15 Damage: 5
Unarmed Strike #2: Attack: 26 Damage: 5