It appears to be some sort of gelatinous membrane. Beyond that, however, it is beyond Petronicus' knowledge. It's not Green Slime, nor is it any of the threatening oozes and jellies which he is aware of. It does not have a magical aura (when he checks). It's strong enough to hold back the water, though the floor appears to be higher than that of the hallway. There is a slight alchemical odour to it, somewhat like rubbing alcohol, though it is hard to tell over the stink of the water.
As he is examining it, Petronicus can see that there are tiny black motes moving around within it.
"You have keen eyes, my learned friend. Gentleman, we have been attacked by many different kinds of swarms. If these motes are yet another, I suggest Mr. Hellblade have his wand ready."
"Mr. Thorthal, would you mind bringing me close enough to test the barrier?"
At the barrier, Haer Kul puts Thorthal into park. "Is everyone ready? I do not know what will happen." He takes a deep breath, and then reaches his hand into the barrier, watching for activity from the motes, and for any sign of movement beyond the barrier.
The barrier slows the explorers' passage a bit, but does not cost any significant effort to get through. It reseals itself after Petronicus, Thorthal, and Haer Kul push their way through.
The floor beyond is covered in a thick layer of crusty, slippery, pale-orange slime, and the air is filled with the odours of rotting vegetation and tar. Lumps of some indeterminate sort lie under the slime here and there.
As the group looks around, a snake made of segmented wood slithers its way out from behind some of the lumps and poises to strike!
It is a construct known as a darkwood cobra, a variant of the more common iron cobra. As well as having standard construct defenses, they are resistant to spells and physical damage. They have reservoirs which may be filled with liquids which are then injected from their fangs.
There is a clicking sound from the wooden segments making up the cobra's body as it rears up and strikes at Thorthal.
bite:1d20 + 3 + 2 ⇒ (12) + 3 + 2 = 171d6 + 1 ⇒ (2) + 1 = 3 I gave the snake a +2 circumstance bonus due to Thorthal's jockey.
The snakes fangs sink into Thorthal's leg, and there is a numbing sensation.
I need a Fort save vs poison from Thorthal, please.
I'd also like a Ride skill check from Haer Kul.
Morgrom sqeezes his two-handed sword in his mighty grip, forcing his way through the green curtain, past Petronicus, "Outta tha way warlock!" He shouts as he makes his way to the empty square in front of the warlock.
Fortitude save vs. Poison:1d20 + 7 ⇒ (17) + 7 = 24
Thorthal will ignore the snakes fangs and attempt to stomp on it, powerfully. Twice.
He will attempt to flank with Morgrom if there is an opportunity, or edge closer to a flank.
Human Male Wizard Lvl:3 HP:19/19 AC:11/11/10 F:+2 R:+2 W:+4 Init:+1 Perception:+10
Petronicus puffs up his chest as he finds some courage. He dangles the crossbow in his offhand as he draws his walking stick and tries to distract the snake to make it easier for Morgrom to hit.
"Petronicus, you shame me." Haer Kul unsheaths his sword cane and slashes at the wooden reptile. "We can at least provide the flank, no?" Attack:1d20 + 1 ⇒ (12) + 1 = 13, damage:1d4 - 1 ⇒ (1) - 1 = 0
Morgrom chops deep into the snake, and Thorthal follows up with a stomp which causes a small crack, but the fury of their attacks is partly absorbed by the darkwood the cobra is made of.
The 4 characters in the room are now in an X formation, all flanking.
Bardos (who now knows that he cannot attack through the green wall)
Petronicus
Snake
Haer Kul
Morgrom
Thorthal
In an outrrrageous Galtian accent: "Ssssssss yourself, you ssstupid ssstickssssnake."
Haer Kul adopts a ridiculous looking fencing pose, and begins to fight defensively (to get the same awesome bonuses on attack that he has on damage): Attack:1d20 + 1 - 4 ⇒ (1) + 1 - 4 = -2, damage:1d4 - 1 ⇒ (4) - 1 = 3