Mazra's Sunless Citadel Campaign

Talking of a rogue, Portia will pull her crossbow out and fire at the creature (I rolled my two rapiers but forgot the pit) 15 to hit, 9 damage (including sneak attack)

Xanth moves into the room in order to make some space. Then Swings at the glowing green thing.

Attack = Nat 20=25   Damage = 18

Offhand attack = 11   Damage = 6

Cast Toll the Dead at glowing green thing, You point at one creature you can see within range, and the sound of a dolorous bell fills the air around it for a moment. The target must succeed on a Wisdom saving throw or take 1d8 necrotic damage. If the target is missing any of its hit points, it instead takes 1d12 necrotic damage.2

GLYNT 20 SMALL GREEN THING 19 ERKY 13 PORTIA 9 XANTH 9 RAGDOR 1

From out of nowhere a SMALL GREEN THING attack XANTH but does not even scratch his boots.

GLYNT covers the SMALL GREEN THING in a lovely hue.

The SMALL GREEN THING tries to claw into XANTH again but only causes a very tiny scratch in his left boot.

ERKY studies the creature intently, curious to know what it is. He has no idea.  Then he realized he should have been attacking the creature.

XANTH slices into the small creature with his glaive, missing the offhand attack.

PORTIA loads and fires a bolt hitting the SMALL GREEN THING.

The creature screaming out something in a terrible language turns into a wisp of smoke and is gone.

It was gone before RAGDOR could finish its spell.

Now what?  Xanth is on one side of the pit and the party is on the other side.

Has the monster teleported away or gone invisible?  If it's invisible the Faerie Fire will still give him away:
"the affected creature or object can’t benefit from being invisible."

If he's teleported or similar I am not sure how Faerie Fire will work as I am concentrating on the spell so I am not sure what happens regarding that if he goes very far away but if my spell ends I should probably feel it (?? - any clarification or ideas here would be appreciated.)

GLYNT will not see his Faerie Fire anywhere.  The spell ends.

ERKY shrugs, "I don't know what that was, nor what just happened."

(If someone in the party can identify the creature, that would help explain more.  Either an Arcana check or Religion check should do it.)

Glynt will try to recall if he's heard anything similar to that creature before - Arcana: 15 

Xanth will look around the room for anymore threats. 

Perception = 13

GLYNT will not know anything about the small strange creature.

XANTH will not see any more threats.

Xanth

"Well okay I think it's gone. I can hold this side of the rope if someone wants to some across."

Ok, so can we tie the other end of the rope to one of the statues in the room?  
Are they sturdy enough to hold the weight of a Dwarf in Armor? I'm guessing that Portia, Esky and Glynt wouldn't be an issue if it can hold Ragdor.

ERKY will say, “I think we should climb down into the pit on this side, and then XANTH can help us with his rope on the other side.  Does anyone on this side have any rope?  I am fresh out.”

The walls of the pit are rough, and they offer handholds to climbers.  With the rope, anyone should be able to do it without an Athletic check.

EDIT: For further clarification, Ragdor has the best Athletic check next to Xanth.  Ragdor could hold the rope on the right side of the pit, Xanth on the left.  Then Radgor would have to climb down without the rope.  I would say that would require a 5 Athletic check.  There would be a small chance Ragdor then would stumble and fall into the pit.  So, there is a risk, though a slight one.  Yet there is the tying the rope to a statue on the right side too.  Then it would be a matter would the statue hold the weight.  I would still require a single Athletic check from Ragdor with the attempt.  A failure would likely mean that the statues doesn't hold and Ragdor slips.

So, do you take this risk?

Arcana - 12. 

"I have rope we can use. I would be happy to try jump across too if I am the last one, but I can't hold much weight so I don't recommend being last."

PORTIA will scour through her memory banks and recall a tale.  She believes the creature was a Quasit.  A small demon.  When destroyed here it simply returned to the Abyss. 

"I am happy to climb down and back up over the other side if the spikes look spread out enough to be safe"

The party should be able to negotiate around the spikes.

Once everyone is ready I am happy to head over to the other room.

"That creature was a demon. It was destroyed but went back to the Abyss where it came from. I am a bit concerned as to why a demon was here."