(Is Trinity attacking the Morkoth or one of the Arcanoloths?)

Seeing the Morkoth, Thorin yells at the Arcanoloth, "That's the thing we've been tryin' ta warn yer's 'bout!" And with that, much like Abzerilan, Thorin dashes after the creature (75ft total movement available, adjust to whatever for the difficult terrain you have).

(DM - if that movement would get me within striking distance, Thorin would use a ki point to use step of the wind to use his bonus action for Dash, then would have an action to attack the creature. But I'm not sure if he'll make it based on your description thus far, so just noting it here in case my understanding is incorrect.)

(I would say that Thorin cannot get close enough to attack with a melee attack, but you can get closer than Abzerilan.)

The Arcanoloths stare at the beast as it runs off, rather dumbfounded and perplexed. It is clear to you that they have never seen such a beast before.

(Is it too late to use Abzerilan's bonus action to cast hunter's mark?)

(No, I would allow it)

Grix also moves toward the Morkoth, instantly throwing his hand out at the creature and releasing a dark wave of energy Eldritch Blast Attack: 20 Damage: 7 and then setting off after Thorin , using Misty Step (as a bonus action) to fade out and reappear another 30 ft closer then using full move to close the distance even more (moving full 30ft adjusted for terrain).

The Morkoth waves one of its free tentacles in front of Grix's Eldritch Blast, turning it aside (casting Shield). It then begins to glow, and with a faint pop, it disappears, reappearing a few hundred feet ahead of you on the slopes (if anyone wants to identify what spell he used, roll Arcana).

OOC: Point of order - how can the Morkoth cast two levelled spells in the same turn?

Arcana check 12

Sorry Trinity would be attacking Morkoth

Quote from MuggsHill >>

OOC: Point of order - how can the Morkoth cast two levelled spells in the same turn?

Arcana check 12

 He has allowed Trinity to do so.

Quote from coachmanak >>

Quote from MuggsHill >>

OOC: Point of order - how can the Morkoth cast two levelled spells in the same turn?

Arcana check 12

 He has allowed Trinity to do so.

( Plus shield is a reaction)

(Yes, Shield was a reaction to Grix's Eldritch Blast. He then cast another spell on his own turn.)

Abzerilan Arcana: 3

"This damnable thing just doesn't want to stay still!" Abzerilan roars as he charges forward.

Grix will Dash after Abz....and if in range will be casting Eldritch Blast (but somehow I don't think we are going to get that close) yelling back to the others  "Trajeon - can you stop that thing, or at least get us closer....?"

What is Trajeon doing, surely he has some more powerful tricks up his sleeve...?

(Grixeor identifies the spell as Dimension Door) (Also, what is the range on Eldritch Blast? The Morkoth moved 200 feet forward, so with your 30 foot dash it's 170 away)

Trajeon nods at Grixeor, who has been following along with the rest of you. He teleports 30 feet closer, then proceeds up the slopes. He extends his finger towards the Morkoth, and a bright ball streaks towards it, impacting the ground just behind the creature with a large explosion.

Morkoth Dex save: 10

Edit: The Morkoth is able to dodge out of the way of the fiery explosion, and it even manages to throw it aside into a large rock up ahead. The rock crumbles, revealing the island you saw in the Old Vaults before the Morkoth escaped the first time. (That was all a reaction from the Morkoth)

Thorin will continue to dash after the morkoth, hoping futilely to reach it before it disappears again.

Range is 120ft so Grix will continue to dash....

Abzerilan keeps running in hot pursuit.

How far away are they?

(They would be 140 ft away after dashing)