Mri'Thas hurls the fluttering imp away from himself and follows up with a magic missile that knocks it spinning. When it rights itself again, one of its tiny legs dangles uselessly beneath it.
While Solon and Ts'iri make ineffectual attacks, Kama'zer and Soldier gang up on the last beetle that blasted them. Soldier beats it into tiny pieces while Kama'zer cheers him on, both of them drawing strength from the experience. The gnome stares, aghast, and screams,
"Another one! You monsters! You murdering BRUTE!" For a moment it's face contorts in rage and it looks as if it wants to strike Soldier dead, but then it draws in a shuddering breath and says,
"Well, you won't kill any more of my beauties!"
The arsonist raises his hands as if conducting a symphony and fire erupts from the ground. A field of hellish flame engulfs the entire southern half of the arena, cutting the heroes off from the two surviving beetles to the north. They brace themselves, expecting an onslaught of pain, but none comes - although the flames put out a terrifyingly realistic amount of heat, they don't actually burn. The field of fire is only an illusion. Still, Kama'zer, Callen and Galinndan find the detail so real they have trouble forcing themselves through the flames - every move comes with an effort.
The arsonist cackles,
"That'll hold you! Try walking through that unscathed! (It seems almost like he doesn't realize it's an illusion.) Then it turns to Solon.
"And you! Get away from my pets!" He grins slyly and makes a strange twisting motion with his hand. One of the beetles rears its head up and makes a strange buzzing click. Suddenly a brilliant flash of flame erupts in front of Solon's eyes, causing him to leap reflexively away - right into the path of the beetle's flaming spew. The blast is aimed perfectly to catch both the Tobari brothers in one shot!
Solon sees what's about to happen and checks himself abruptly. The gnome hisses in disappointment and runs off backstage, halting safely around the corner from Ts'iri.
Obedient to its master's command, the beetle twists its head to point at Solon and sprays its fire anyway, catching him full in the face but sparing Goeth. Solon screams and collapses as his skin blisters and and cracks under the onslaught. The flames die down in an instant, but his breathing grows ragged and his body shudders as he clings to life.
His attacker scuttles away beneath the benches, just as the second beetle spits forth its own blast, which washes harmlessly above Solon's body and catches Goeth in the backwash, burning him only slightly. The imp hovering above Solon is caught in the crossfire of the two blasts, but it merely dances and spins in the air, cackling in delight as the flames wash over it. As the flames die away it is gone, but a brief eddy in the smoke marks the path of its invisible wings as it flies away.
[sblock=Passive Perception 11]
Although you can't see it, you can hear the Imp 1's tiny wings beating at K12. Also, if you look very closely, you can occasionally see a puff of flame that still dances on its body, although it's hard to distinguish from the embers that are floating in the air.
[/sblock]
OOC: anyone who spends a minor action during their turn to search for Imp 1 can roll an active Perception check, and read the above block if they roll 11.
The beetle facing Ts'iri rushes towards her and clamps onto her leg with its mandibles, but it only leaves a slight gouge in her leather armour. Another beetle comes around the corner and, unabled to get close enough to bite, opens its jaws and lets a blast of red flame wash over its companion toward her. The beetle is unaffected, and Ts'iri herself takes miraculously little damage thanks to her fiendish fortification.
The remaining imp swoops towards Mri'Thas again and lashes at him with its tail, scoring a bloody line across its cheek. He feels the sting of its poison, but the wound is not deep enough for it to enter.
A few more scattered fires spring up at the base of the stage.
[sblock=Status]
Mri'Thas shifts to R14 and hits Imp 2 twice, pushing it to P14 and doing 35 total damage. That bloodies it.
Kama'zer heals Soldier for 24 (no longer bloodied) and herself for 11 (no longer bloodied), then attacks Beetle 5 for 6 damage.
Ts'iri shifts to J20, misses Beetle 2, and gains 9 temp hp.
Solon heals himself for 8 (no longer bloodied), puts a Divine Challenge on Beetle 1, and misses it with Holy Strike.
Soldier moves to N8 and hits Beetle 5 for 12 damage, killing it. He saves against dazed.
The Gnome Arsonist casts Illusory Terrain, a close burst 5 centered at P12.
11 vs Soldier (miss), 18 vs Kama'zer (hit), 10 vs Mri'Thas (miss), 17 vs Callen (hit), 22 vs Galinndan (hit). Kama'zer, Callen and Galinndan are slowed (save ends).
It uses an action point to cast Startling Glamor at Solon,
missing with a natural 1. (The intent was to move him to E8 so that Beetle 1 can hit both him and Goeth in one blast, but that failed.) Then it moves to G18 - only Beetle 2 and Beetle 4 are in its Heat Haze now.
Beetle 1 sprays fire at Solon,
critically hitting for 18 fire damage. This takes him to -1 - he's now dying. Then it moves to I8 (it can only move 3 because the pews are difficult terrain). (Almost forgot, the blast
also hits Imp 1 with a 22, for 9 fire damage, which is nullified by its fire resistance.)
Beetle 2 moves to I20 and bites at Ts'iri,
missing with a 7.
Beetle 3 sprays fire at Solon, Goeth, and Imp 1, hitting
hitting Solon with 15, hitting Goeth with 17, and hitting the imp with 18. This does 10 damage to Solon and Goeth, and 0 to the imp due to fire resistance. (The roll in invisible castle is accidentally labelled "Beetle 1". Also, a 15 hits Solon because, being unconscious, he grants combat advantage and takes -5 to all defenses.) Then it moves to E8.
Beetle 4 moves to H20 and sprays fire at Ts'iri and Beetle 2,
critically hitting Ts'iri for 18 fire damage, and hitting Beetle 2 for 9 fire damage (0 after subtracting fire resistance). Ts'iri's temp hp are gone and she takes 9 more damage.
Imp 1 turns invisible and moves away. (This causes its Tail Sting to recharge.) It rolls an
11 Stealth (link says 16, but I forgot that the -5 for moving cancels out the +5 for being invisible), so only people with an 11 Passive Perception, or who spend a minor action and roll higher than 11 Perception, know where it is.
Imp 2 moves to R14 and attacks Mri'Thas with Tail Sting,
hitting with a 23 for 7 damage. It makes a secondary attack for the poison,
missing with a natural 1.
Almost forgot,
the fire continues to spread. A roll of 2 on 1d2 means that square spreads, the d8 gives the direction. This turns, H9 spreads east (no effect since H10 is already on fire), H10 spreads south to I10, and K10 spreads southeast to L9.
The big double doors at Q3/R4, and the doors at B5, F14, N20 and U12 are open. The door at H18 is destroyed. The rest are closed.
Callen's turn!
26 -
M - Mri'Thas (
28/35 hp)
23 -
K - Kama'zer (
18/31 hp, slowed (save ends))
11 -
T - Ts'iri (
26/35 hp, concealment until EONT)
9 -
S - Solon (
-11/25 hp,
dying)
9 -
W - Soldier (
25/36 hp)
9 -
A - Arsonist (
11 damage, concealment due to Heat Haze)
8 -
B1 - Beetle 1 (
28 damage, cursed by Goeth, marked with Divine Challenge by Solon, used Fire Spray)
8 -
B2 - Beetle 2 (
9 damage, concealment due to Heat Haze)
8 -
B3 - Beetle 3 (
0 damage, used Fire Spray)
8 -
B4 - Beetle 4 (
0 damage, concealment due to Heat Haze, used Fire Spray)
8 - B5 - Beetle 5 (39 damage, used Fire Spray, prone and immobilized until end of next turn, provokes an OA from Soldier if it shifts before the start of Kama'zer's next turn)
8 - B6 - Beetle 6 (36 damage)
8 - B7 - Beetle 7 (38 damage, used Fire Spray)
8 - B8 - Beetle 8 (32 damage, used Fire Spray)
28 -
I1 - Imp 1 (
0 damage)
28 -
I2 - Imp 2 (
35 damage, used Tail Sting)
7 -
C - Callen (
28/28 hp, slowed (save ends))
5 -
G - Goeth (
24/34 hp)
4 -
R - Galinndan (
29/29 hp, slowed (save ends))
[/sblock]

Imp 1 is not on the map because it's invisible. The shaded square shows the area affected by the gnome's Field of Fire illusion - it has no further effect, it's just there so you can see who was hit.
EDIT: I accidentally recorded Mri'Thas's damage twice, on both imps. Imp 1 is actually unhurt. Fixed in the status.