Rasa flies to head off the spiders. He sends a small seed of fire into the tunnel, and that seed blossoms into a booming fireball! 

26 fire damage

Saves: 7, 8, 17, 6

Rasa holds for applause. 

Sparky, Rasa's wildfire spirit, flies into the cave, burning through some of the icy web sheets and launching a flame seed at the ice spider in its lair: Attack: 9 Damage: 5

Swiper gives Rasa an applause! But then stops once he realizes that Derrikoth is still under attack!

Pew pew! Attack: 18 Damage: 12
Snekay: 12

Con Save: 7

Derrikoth cuts at the webs, swinging at the giant spider if he manages to cut himself free.

Attack: 15 Damage: 6

Attack: 16 Damage: 4

Dis for the 2nd attack if the first doesn't get the job done: 18

Nirzeg gives the tunnel behind him a quick but worried look upon feeling the wave of heat sweep in behind himself. "Talk 'bout ****'n killing with extreme prejudice... I like your  style my fire toned feathered ally!" He calls back to Ah'brasar. "Now for you." He says, having snapped back around with two fingers extended at the spider. Conjured into being in a subtle but tight gesture is a bead of fire that rockets off just inches from finger tips for a leg of the beast.

Having done his civic duty, Zeek spends his time cowering behind friend Swiper.

Action: Cast Fire bolt - Attack: 24 Damage: 2 of Fire on Omega Spider Prime.

Lydia casts Toll the Dead on the spider. DC15 Wisdom save or take 13

WIS save: 16

This last spider fights differently than the others—more desperately, perhaps. She lunges at Derrikoth The Greater, taking a bite at him after he managed to break her webbing. 

Lair Action Bite Attack: 24 Damage: 8 and on a hit, Derrikoth must make a DC 11 CON saving throw. He takes 12 poison damage on a failed throw, or half as much on a successful throw.

Lair Action Web Attack vs Sparky: 13 on a hit, Sparky is restrained. 

The spider then bites at Derrikoth.

Bite Attack: 13 Damage: 11 and on a hit, Derrikoth must make a DC 11 CON saving throw. He takes 11 poison damage on a failed throw, or half as much on a successful throw.

Derrikoth receives 4 cold damage at the beginning of his turn. 

// Players up! //

Corn: 15

Derrikoth brings his sword down on the spider, testing out his newfound size.

Attack: 23 Damage: 8

Attack: 22 Damage: 13

He takes a deep breath, regaining some stamina. (Second Wind: 16)

“Damn this ***** wont quit!” Swiper shouts in irritation as he loads up another shot at the spider!

Attack: 19 Damage: 9
Sneeeeew: 15

Grudgingly at Nirzeg's mental command, Zeek flies over the corpses of spiders to circle around to the other tunnel the long way around, confirming whether it truly be a shortcut or not. Meanwhile, a dissatisfied Githyanki tries to put more zest into his next conjuring of flames, though his aim remains ever focused on sides and limbs, rather than the spiders money makers. He had much to harvest at the end of this, and spoling that would simply not due!

Action: Cast Fire bolt - Attack: 24 Damage: 16 of Fire on Omega Spider Prime.

Nirzeg’s flames finish off the giant spider, and it collapses against its own webs. As it falls, there is a crushing sound, and swarms of tiny white spiderlings come crawling toward you from underneath the slain ice spider!

// Lydia is up //

Lydia casts Thunderwave.

DC15 or the spiders take 8

Lydia's spell squashes lots of the spiders as they begin to swarm all over her and Derrikoth. It also shatters the majority of icy webs in the cavern, revealing what looks to be a potion bottle on the frozen floor, lying next to a beautiful warhammer.

Lydia and Derrikoth are now covered in swarms of little spiderlings, and the critters are hungry.

Bite Attack vs Derrikoth: 21 Damage: 8 piercing

Bite Attack vs Derrikoth: 17 Damage: 9 piercing

 (Forgot about the pushback, this swarm doesn't have quite enough movement to reach you this round so can't attack. But it's crawling for Derrikoth) 

Bite Attack vs Lydia: 10 Damage: 12 piercing

// Players up! //

"You have got to be shi-..." Nirzeg catches himself, and quirks a brow. "Actually... This could be good... This could be very, very good..." A sly smile blooms as he again looses another bolt of fire. Though this time, he directs at those that have thus far managed to reach Lydia for her safety as Zeek loops around for a better position... and totally not because Nirzeg minded grazing her less than he did that of Derrikoth, his buddy and pal.

Action: Cast Fire bolt - Attack: 10 Damage: 13 of Fire on Spiderswarm attacking Lydia.

"Get off me friend, ya bastards!" Swiper shouts angrily, swapping out his crossbow for his swords, then attacking the swarm on Lydia as carefully as possible!

Attack: 22 Damage: 8
Attack: 25 Damage: 7
Sneaky Panchos: 8

 Lydia swings her hammer at the spiders attacking her.

Attack: 11 Damage: 10

Working together, the three of you (Lydia, Nirzeg, and Swiper) manage to squish all the little baby spiders trying to eat Lydia. However, there are still many tiny little spiderlings crawling all over Derrikoth.

Rasa attempts to follow Nirzeg's example and produces a flame, which he uses to burn the spiders! 

Fire Attack: 19 Damage: 20 fire

He commands Sparky to do the same...

Flame Seed Attack: 17 Damage: 3

Rasa and Sparky incinerate about half of the tiny little crawlers. 

// Derrikoth is up! //

"AAAAAH! Get off me, filthy cretins!"

Derrikoth flails around with his longsword, attempting to cleanse himself of spiders.

Attack: 21 Damage: 8

Attack: 13 Damage: 9

The enlarged Derrikoth's flailing is surprisingly effective. The spiders are scraped off and crushed underneath his double-sized feet.

There is no more scuttling or scurrying in the frozen cavern. You have slain the spider queen and her progeny, though there are more tunnels to explore. 

// Where do you wish to go from here? //