Gerrard:

Using his rapier to parry the first attack, Gerrard says laconically, "Well, I did try to save your lives."   The young noble launches into a rapid series of strikes with his flaming dagger and glowing rapier on the creature who just attacked him, transitioning to the other adjacent one if the first one falls.

Reaction to Parry:  7

Attack Action:

Flaming Dagger:  Attack: 22 Damage: 19

Flaming Dagger:  Attack: 22 Damage: 12

Flaming Dagger:  Attack: 23 Damage: Unable to parse dice roll.

Bonus Action Rapier:  Attack: 20 Damage: 11

(Action Surge)

Flaming Dagger:  Attack: 25 Damage: 15

Flaming Dagger:  Attack: 11 Damage: 14

Flaming Dagger:  Attack: 13 Damage: 18

Kei 

Turning at the sound of the hissing voice, Kei sees his friend being assailed from near and far. "Unacceptable" he growls through his teeth. Instinctively he reaches for his deck of cards only to find that pouch long gone. A well of anger builds inside him as the shadows themselves seem to leech off the walls. They form a twisting pattern on the far side of the warehouse, enveloping Gerrard and the three lion creatures. In a split second the room returns to normal but the swirls and shapes made by the shadows linger in the minds of those it encompassed.

A - Hypnotic Pattern (with WIS17 save) using Careful metamagic to give Gerrard an auto save.

Once the room returns to normal he moves to the centre of the room and speaks loud enough for both Boko and Gerrard to hear. "If they look dazed or confused, leave them be. Trust me."

M - move so as he has a clear line of sight of the "lions", somewhere near the centre of the room - perhaps slightly left of dead centre.

In a flurry of blades, Gerrard tears through the manticore that attacked him, nearly cutting it to ribbons. It is bleeding and badly injured.

Then, a twisting, hypnotic pattern of colors weaves through the air around Gerrard and the three flying creatures. Gerrard is insulated from the mesmerizing spectacle, but his three attackers are momentarily transfixed. DC17 WIS Saves: 15, 9, 3 

His two immediate attackers shrug off the effects, but the third manticore – the one that fired tail spikes at Gerrard – drops to the ground, mesmerized by the swirl of colors.

Boko is up! She is about 60' from the winged, lion-like monstrosities.

Boko looks out of the office and moves forward to be in position to cast faerie fire on just the lion-headed creatures (DEX 17 saves) and not Gerrard.

She then takes cover behind a crate near the main doors.

Boko releases a bloom of violet light around the manticores as she ducks behind a crate (half-cover.) DC17 DEX Saves: 17,  14. (The hypnotized one automatically fails.)

Both manticores aloft attempt to tear into Gerrard:

#1 Bite Attack vs Gerrard: 7. Hit: 9 piercing damage.
#1 Claw Attack #1 vs. Gerrard: 7. Hit: 4 slashing damage.
#1 Claw Attack #2 vs. Gerrard: 7. Hit: 8 slashing damage.

#2 Bite Attack vs Gerrard: 14. Hit: 11 piercing damage.
#2 Claw Attack #1 vs. Gerrard: 16. Hit: 9 slashing damage.
#2 Claw Attack #2 vs. Gerrard: 20. Hit: 4 slashing damage.

Everyone may act. (Kei and Boko both still concentrating.)

Manticores #2 and #3 glow with an unnatural violet aura (advantage on attacks against them.)
Manticore #3 is on the floor, gazing motionlessly into the swirl of colors (incapacitated and charmed.)

Gerrard:

Parrying the hit from the manticore, Gerrard continues to attack the one he started on!  If the first one falls, he attacks the next one.

(Not sure if the injured one is currently affected by Faerie Fire, so rolling advantage separately).

Fiery Dagger Attack:  14  26

Damage:  12

Fiery Dagger Attack:  28  14

Damage:  15

Fiery Dagger Attack:  24  22

Damage:  14

Bonus Action Rapier:  24  17
Damage:  7

Kei 

With Boko's purple haze now settling over the battlefield and Gerrard's furious strikes sparking inspiration within him, Kei unleashes more dark energy in the form of shadows streaking from his fingers towards manticore #2.

Blast 1 Attack: 29 Damage: 16

Blast 2 Attack: 24 Damage: 11

Blast 3 Attack: 20 Damage: 11

With a final swipe of his fiery blade, Gerrard fells the glowing manticore in front of him. It falls to the floor with a heavy thump, quite dead.
He then turns his attention to the uninjured one one unaffected by the eerie violet glow, and tears it up with three powerful blows. It is quite injured.

Shifting his attention to manticore #1, Kei unleashes a trio of crackling black beams at the injured monstrosity, hitting it with all three. It is badly injured, roaring with pain and anger.

Boko is up next!
(One badly-injured but non-glowing manticore is still harassing Gerrard. The other, glowing, one, sits peacefully on the floor, silently watching Kei's mesmerizing lights.
Boko is still concentrating on Faerie Fire.)

Whammm!

A huge, red, froglike creature with massive, curled claws crashes to the floor, crushing one of its legs. A shattered bone protrudes from its shin. It screams in pain and anger and exhilaration. (Bludgeoning damage: 7) 

You hear a low, unnerving voice in your heads. "What is this? What is happening?"

Everyone may act.

Meanwhile, the badly injured manticore tries to tear into Gerrard with renewed, desperate fury.

#1 Bite Attack vs Gerrard: 18. Hit: 8 piercing damage.
#1 Claw Attack #1 vs. Gerrard: 24. Hit: 6 slashing damage.
#1 Claw Attack #2 vs. Gerrard: 10. Hit: 6 slashing damage.

The newcomer with the crushed, bleeding leg looks around, confused, a horrid grin on its face. "Trespassers?"

Everyone may act!
Boko and Kei continue to concentrate on their spells. Gerrard's attacker is badly injured; the hypnotized manticore remains still and incapacitated. The wounded leg of the red froglike aberration is beginning to heal itself.

Gerrard:

”Hey, stay out of my head!  I’m busy fighting the lion-man!” says Gerrard as he parried the attack from the manticore.

Parry:  8

He then lights into the foe tormenting him!

Flaming Dagger:  Attack: 29 Damage: 9

Flaming Dagger:  Attack: 25 Damage: 16

Flaming Dagger:  Attack: 10 Damage: 13

Bonus Action Rapier:  Attack: 21 Damage: 13

Kei 

The newcomer to the battlefield gives Kei a start. "Where'd you come from?" he asks rhetorically as he watches Gerrard coolly switch targets. Not wanting his friend to get overwhelmed he launches another barrage of shadowy beams at the manticore. In the same heartbeat he draws on his inner strength and curses the frogman with words from a famous witch.

Action - EB at the manticore. If it goes down, remaining blasts at frogman.

Blast 1 Attack: 25 Damage: 9

Blast 2 Attack: 11 Damage: 11

Blast 3 Attack: 15 Damage: 11

BA - Quickened Tasha's Mind Whip on the frogman for 11 psychic damage and the rider effects. ½ damage and no rider on a INT17 save.

Gerrard shreds the manticore with a flurry of slashing blades. It falls to the floor, quite dead.

Kei turns his arcane attention to the huge red horror that dropped from above, firing three beams of crackling energy at it. It shrieks in pain as all three drill deeply into the horrid creature.
Then the psychic lash hits. DC17 INT Save: 7

It staggers, holding its head, then bounds toward Kei in a savage, furious frenzy.

Everyone may act!

Gerrard:

Moving up quickly behind the red frog-like creature, Gerrard tries to give him someone else to target besides Kei.  Seeing the leg injury begin to heal, the young noble decides to try and capitalize on the creature’s injury before it can heal.

Stabbing furiously with his fiery dagger and moonlit rapier, Gerrard attempts to tangle up the creature’s legs as he attacks!

(Include a trip attempt on the first hit.  If the foe fails a DC 17 Strength Save, it is tripped and subsequent adjacent attacks are at advantage).

First attack hitting does extra damage= 8 and activates trip.

Fiery Dagger:  Attack: 20 Damage: 18

Fiery Dagger:  Attack: 26 Damage: 13

Fiery Dagger:  Attack: 18 Damage: 12

Glowing Rapier:  Attack: 19 Damage: 7

(Extra attack rolls if needed for advantage:  16     26     27  )

Kei 

It feels good to be sliding back into sync. The thought flashes through Kei's mind as he witnesses Gerrard slash through the frogmans hide in his defence. He takes the moment of distraction to slip back from the amphibian. Once about safe from the frog he presses his two forefinger to his temple and directs his gaze and thoughts at his enemies face.

M - 30ft SW between two boxes that are diagonal to each other.

A - cast Mind Sliver INT17 save or take 11 psychic damage and subtract 4 from next save.

Gerrard sprints after the red frog thing, slashing it with a fiery dagger before attempting to topple it from behind. (It is evidently resistant to fire... but not to blades.) DC17 STR Save: 18

And down it tumbles. Gerrard leaps on the huge horror, raining down fiery blows upon it, wounding it badly with his blades.

DC 17 INT Save: 12