The rocks seem to move towards you.  Roll initiative. 

Initiative: 24

4

"The stones are moving now? The last time I saw that was a good 5 years ago!"

6

Initiative: 8

"Moving wet rocks...I have a feeling these are not friendlies, make ready"

Un'undeen Initiative: 5

"Why in all hells are the rocks moving?"

Feltorius casts faerie fire on the moving rocks, one of which then lunges in the general direction of the party, landing in an amorphous heap. 

Captain Danwin dropped his torch and pulled the Greatsword from his back, "Rock meet steel, cold, hard, steel!" Captain Danwin raised his sword and brought it down on the Amorphous rock. 

Attack with Greatsword: 17 

Damage with Greatsword: 15

Second Attack with Greatsword: 18 

Second Damage with Greatsword: 14

Advantage on Second Attack with Greatsword: 10

"unable to parse die roll"

Un'undeen takes a careful step back as one rock lunges forward before being struck down viciously by Captain Danwin.
"Well done, Captain," She exclaims before going into a short arcane incantation, the floating crystals around her head growing slightly brighter as she does so. She raises her hand up as if clutching an apple, meaning to squash it, while a sudden batch of snow and frost starts climbing up the second rock. When she finishes, her diadem flashes once and dims as she surveys her handy work.

[Frostbite: DC15 Con save for 12 Cold Damage and Disadvantage on its next attack.]

Whether it takes effect or not, Un'undeen repositions herself to put every other party member between her and the strange lumps.

Malekai follows suit in the Captain's wake, lunging with his rapier towards the second rock. An odd sensation runs up Malekai's arm as his rapier pierces into the wet rock, but he ignores the feeling as best he can as he retracts the blade. 

The Tiefling gathers his bearings after striking into the wet rock and then disengages away from the odd creature.

Malekai's rapier comes out dripping some sort of gray goo to the accompaniment of a faint sizzling sound. 

Usmor casts fire bolt, but altered to deal thunder damage, so a focused wave of sound bursts from his hand to the rock.

15

9

The second rock stops moving and flattens out, melding with the first to form a large puddle of what now appears to be oil. 

Un'undeen takes another careful step backwards as the oil like substance spills forward. She keeps as far as she can from the pool as it settles. Then she takes out a bolt from her satchel and dips its tip into the murky liquid. She swirls it around a bit and then lifts it up in front of her, keeping it safely away from her body.

The bolt dissolves quite rapidly. 

"Nasty stuff," Un'undeen says with a touch of chill in her voice as she lets the bolt slip under the surface of the liquid. "Nobody really touched it, right?" She asks around.

It's there any visible exits? Where did the rocks come from? It's there a safe way around the pool? If there are no exits, Un'undeen stats looking for one.

There is the entrance to a tunnel at the far end of the cave. 

Usmor decides to enter the tunnel.

Anyone else entering the tunnel?  It's the only visible opening.