In the frantic fight Ed's dagger misses

Watching in disbelief as the shot does almost nothing James desperately fires the revolver again with the muzzle against the abomination's temple.

Revolver: 25 Piercing damage: 16 + 7

Lola, bolstered by the swig she's just taken from the flask, steps forward until she can see the creature clearly. She pulls yet another contraption from her pocket, straps it onto her arm, yells a strangled word that may or may not be "Go!" and shoots fire onto the back of the creature. 

Movement: moving into line of sight but keeping distance

Action: cast Fire Bolt (artificer style)

Attack: 15 Damage: 8

Bonus Action: none

Wis save 25

Both James and Lola hit.With James blowing hole in de Mendoza's head. He still stands, but the fire is disrupts his regeneration

Round 3.

Tired of being shot he turns to James and tries to grapple him

Athletics - 11

He then tries to bite James

Attack: 14 Damage: 5 piercing damage

Plus 5 necrotic damage

Now its the party's turn

Seeing the creature attack James, Edward pulled out another dagger. "Back off, monster!" he growled as he lunged towards de Mendoza.

FREE: Draw another dagger
ACTION: Attack de Mendoza with the dagger
* Dagger Stab - Attack: 22, Damage: 6 mundane piercing (add 2 on a crit)
BONUS: Attack de Mendoza with the first dagger
* Dagger Stab - Attack: 8, Damage: 4 mundane piercing (add 3 on a crit)
EXTRA: On the first hit, use Psionic Strike to add 5 force damage to the attack

Two psionic die used; end of turn!

Lola keeps yelling, trying to bathe the creature in fire without hitting the others. 

Movement: only into line of sight, but staying back if possible

Action:

Cast Fire Bolt Attack: 19 Damage: 5

Bonus action:

(Cast Healing Word on James. 6 HP healing) To do this, she throws him some antiseptic powder to pour on the wound. "Hey! James! Put this on the wound - it'll help, I promise!"

James acrobatics to resist grapple: 18

Gritting his teeth at the pain of the Mendoza-abomination's maw sinking it's teeth into his flesh, the british gentleman again fires the revolver, putting another bullet into the creature's disgusting head.

Revolver: 18 Piercing damage: 11 + 3

He then catches the small box containing powder and quickly applies it to his wound.

Nice everyone landed a hit and the damages are mounting as de Mendoza can no longer regenerate

Round 4

You see de Mendoza fingernails lengthen and sharpen to a point. He swipes at James with his claws and goes for a bite

Claw - Attack: 9 Damage: 8 slashing damage

Bite - Attack: 13 Damage: 6 piercing damage

Plus 9 necrotic damage

Now its the party's turn

James spends his turn dying in a puddle of his own blood. :-P
Death save: 21

"Not good," thought Edward grimly as their opponent took James down. "Save the Brit!" he yelled to Lola while he lunged at de Mendoza again, trying desperately to finish him off--or at least drive him away--before they all met their maker.

ACTION: Attack de Mendoza
* Dagger Stab - Attack: 24, Damage: 5 mundane piercing (add 2 on a crit)
BONUS: Attack de Mendoza again
* Dagger Stab - Attack: 12, Damage: 4 mundane piercing (add 2 on a crit)
EXTRA: The first hit will use Psionic Strike to add 6 force damage

Three psionic die used; end of turn!

Lola grits her teeth and tries the flame-thrower on de Mendoza again.

Action:

Cast Fire Bolt Attack: 11 Damage: 9

Movement: run to James' side to treat him.

Bonus action:

(Cast Healing Word on James.  HP healing 7 ) She grabs out a roll of bandage and a handy stick from her capacious pocket and starts to splint and bind up his wound.