@OldMan, that's how I understand the spell - I think you did it right. 

As Klarg sees his pet Ripper fall in battle, he lets out a vicious roar, "NOOOOO! RIPPER! YOU WILL REGRET THE DAY YOU CROSSED KLARG!"

At that and realizing he's now alone and outnumbered, he turns and makes for the natural chimney, descending easily for such a large bugbear (athletics check 15; DC was 10 to successfully descend). He runs through the Kennel, retreating toward the cave entrance.

What would you all like to do? You can make chase and try to kill him or you all can let him go. It's technically Bearkiller's turn if you want to make chase.

(Galben looking around at the group)

"I don't think many of us could fit through that crack let along run him down...especially you OldMan."

(Galben collects the short bows, quivers and arrows from Goblins 4&5 as well as the scimitar from Goblin 3 and sets them next to the opening they came through. Then he starts looking through all the supplies, boxes and barrels in the room and finds...)

"We must catch him, we need information! " Jake hastily urges the group. "There are six of us and one of him, we can do this!"

"If a Bugbear can fit so can we, we have the momentum, we ought finish this!"

"If you say so, I'm behind ya" (Galben moves towards Jake)

OldMan agrees we need to go get him.  We have the momentum and several of us are fleet of foot (maybe not the armored ones).  Remember Galben that I am old only compared to these youngling humans.  Being an elf like you we live for generations of humans.  

I think Bearkiller, Galben and I should pursue the beast quickly through the crack with the armored caravan taking the safer route through the cave.  We don't know for sure that he is exiting the cave.  He may try crossing the bridge or even try flanking us by coming back into this room from the stream.  Hopefully the Three of us can keep him occupied enough until the armored cavalry arrive.

Jake takes note of what OldMan has said, looks to Thallan and Regula, and then sprints back down toward the waterfall room.  Before he leaves, he taps Galben on the shoulder to cast guidance, "May Ilmater guide your arrow swift and true."

(Galben gives a nod to Jake and moves behind Bearkiller, preparing to make his way through the chimney crack)

"Let's track Klarg down!"

OldMan hikes up his robes to ready for the descent.  Ready to follow Galben and Bearkiller into battle.

Anybody descending the chimney can make an athletics check and post the result now . Anybody going around the long way - we will say it takes two turns to get there. If you go down the chimney successfully (10 or higher on athletics check), you can use your attack immediately as well as movement doesn't count as action during combat.

(Galben runs to the chimney)

(Athletics roll:18) He slides through and starts looking for Klarg. (He readies his bow with a nocked arrow if he should be attacked)

(Galben takes aim and lets the arrow fly, Attack roll 13+5=18: Piercing damage 2+3=5. The arrow sticks Klarg in the back of his arm slowing him a little but not enough to bring him down.)

OldMan rolls Athletics: 19+2=21 also rolls Acrobatics 16+4=20.  

OldMan slides gracefully down the embankment catching his foot about 3 feet above the dog kennel floor and uses his momentum to do a flip in the air landing gracefully in a crouched position.  He instantly casts  Firebolt at the cowardly goblin leader 11+6 = 17 to hit. (can't remember what is needed and it's on previous page of posts) but if it did hit I rolled a 7 for damage.

OldMan realizing his spell hit Klarg square in the back,  decided to yell insults at the monster to try to trick him into pausing therefore giving the rest of the group time to catch up.

"Hey Klarg!  I heard your father mated with a Mind Flayer but you're too stupid for that combination!  Maybe he did it with a Roper!  Probably just got an Orc whore drunk enough to put up with his stench, based on yours!!!  The pup is always like the sire!"

(Galben turns his head towards OldMan and starts laughing at his verbal assault)

Thallan shimmies down into the space, (Athletics 4+6=10) nearly slipping but managing to descend without malady, Springing to his feet and giving chase, (Acrobatics 19+3=22) closing with the group. (not sure if I am able to attack or not)

Thallan, since you made it down the chimney successfully, you are able to take an attack upon entering the room! Rest of the party, feel free to post whether you'll try descending the chimney or going around.

By my count, Klarg has 15 hp left.

Regula confidently walks to the chimney, jumping gracefully into the vertical shaft, expecting to catch his foot on the craggy projections; however, his foot completely misses and he falls to the bottom of the chimney (crit fail; takes 4 bludgeoning damage [1d6])

Standing and dusting dirt off his armor, I say: "It might not have been pretty but it was quick and direct."

Thallan finding an opening, thrusts his blade into the Bugbear, (HD 12+6=18, Dam 5+6=11) the beast howling as hammer forged steel penetrates his torso, green blood cascading down from the wound.

(Galben looking at Thallan, OldMan and Regula)

"We need him alive to question him!" (When you attack him and hit say you are trying to knock him unconscious, then we can questions him)

https://www.dndbeyond.com/profile/MontiHodor/characters/66856223

Here is my character sheet FYI