Quyst blasts the beast and then finds partial cover behind a tree. Renewal sends three streaks of flame at the creature. One of the rays finds its target.
2nd Attack roll: 11 3rd Attack roll: 17

(Bram is prone but not restrained. He can take his turn as normal, although it takes half his movement to stand up.)

Managing somehow to wiggle free, Bram rolls to his feet, pulling up his ebony crossbow as he exhales heavily in desperation.  If he's not in range of an attack of opportunity, he will move away from the creature, but if movement would provoke one, he'll stand his ground.

Bonus Action: Healing Wind 7

Attack: 22
Damage: 9

Superiority Dice: 8 for Precision if it missed or additional damage and Menacing Attack if it didn't

Feeling pretty desperate, Bram also calls upon his reserves to perform an Action Surge: 

Attack: 19
Damage: 8

While spending another Superiority Dice: 7 for either Precision if it missed, or Menacing if the first time didn't sink, or Trip if the creature is now frightened

Bram stands up and fires two bolts at point blank range into a gap in the bulette's armour. The beast howls in pain and snaps at Bram with a huge beak.

Attack: 8 Damage: 29

Temporarily blinded by pain, the bulette takes a large bite out of the ground instead of biting Bram in half.

(Everyone is up.)

Staring at the monstrous creature, Tansiar whispers words directed at it.

OOC: Cast Dissonant Whisper on the monster for 13 Psychic Damage Wis DC 14 for half. If failed, it also runs away from me.

Dissonant Whispers WIS Save: 1
Menacing Attack Save: 2
Trip Attack Save: 21

The beast runs away in panic, allowing Bram and Tafod to strike as it runs 40 feet away.

(Bram and Tafod may take AoOs. Bram would have to use an unarmed attack since he’s not currently wielding a melee weapon.)

(Bram, Quyst, Renewal, Tafod)

(Would Bram be able to make a melee attack with his crossbow due to the Crossbow Expert feat, meaning he can quickly attack and at 5ft range with it?)

Bram, seeing the creature fleeing, tries to bash it with his shield (unarmed attack), and then takes another couple of shots at it:

AOO: 6
Damage: 2

Crossbow Attack: 21
Damage: 9
Superiority Dice: 2 Precision or Trip

Bonus Crossbow Attack: 27
Damage: 8
Superiority Dice: 3 Precision or Trip

The bulette is severely wounded by Bram’s shots.

STR Save: 6

The bulette falls prone to the ground, unbalanced by the force of Bram’s arrows.

(Quyst, Renewal, Tafod.)

Chop!  Tafod swings his greataxe with force.

Attack: 10 Damage: 9  (+2 rage dmg)

And starts digging up daisies.

(psst Tafod if it's on the ground you gots the advantage, reroll dat attack!)

Okay, with advantage then:   Attack: 23 Damage: 13

"Wes loiks tha' mooch better."

OCC Thanks mate!

Quyst shoots the creature again: "No running away after hurting us, monster!"

Eldritch blast: 15; dmg: 3 + 4

Okay, Tofod will hurl a javelin then.

Attack: 19 Damage: 12

Tafod swings are the beast as it runs away, then throws a javelin, but neither connect. Renewal sends three fiery tongues to lash out at the bulette.

Attack: 5 Damage: 6
Attack: 5 Damage: 7
Attack: 8 Damage: 4

None of them connect. The injured bulette stands up and, throwing chunks of dirt behind it, burrows twenty feet into the ground, leaving a gaping hole behind it.

(Everyone is up.)

"Bleedin', stinkin', backstabbin' cowardly bugger!" Tafod curses vehemently as he seeks to retrieve his javelin. "Sneakin' son of a queen's arse licker, bloomin' pile o' dog excrescence!"

Bram runs towards the hole the creature burrowed into and dives in, sliding down the slippery slope.  He can't see anything in the darkness, but still fires into the tunnel, hoping that he might connect with something and stop it from popping back up somewhere else.

Attack with disadvantage XD: 18
If by some miracle that hits, 5

More of the same with disadvantage: 17
If it were to hit, 5

If he has any movement left after that, he's going to try to start climbing out of the hole.

Quyst looks around for any high ground where the monster wouldn't be able to catch her from the ground - a tree she can easily climb, or a boulder, something like that.

"Try to get safe, guys, this thing is likely to come back!"

If she has enough time, she'll also cast Mage armor on herself

Tanisar will inspire Bram, but remain still.

(1d6). For 10 minutes, the creature can add it to one ability check, attack roll, or saving throw. This can be added after seeing the roll, but before knowing the outcome.

Bram definitely adds an inspiration to his attack: 3

Renewal sends a bolt of flame into the hole the bulette is digging.

Attack: 22 Damage: 7

It fails to penetrate the beast’s armour.

The bulette rapidly digs through the earth. The earth around it falls in, covering it and hiding it from view. The tremors in the ground disappear as it flees from you.

(Congratulations! You each receive 360 XP!)

The bulette is gone. It’s warm, almost stifling, under the canopy of the forest, and not a breath of wind stirs. As you pause to gain your bearings, peering into the forest gloom, you hear a voice, “Hold there, strangers! We would speak with you.”
A moment later an elf dressed in a short tunic of brown and green steps into the open and advances toward you, a bow in his hand. “I am Israfen of the Woodsingers,” he says. “I see that you are not Harkenwolders, and you do not look like the mercenar- ies of Iron Keep. Who are you, and what is your business in the Harken Forest?”