Round 2

16 Sphinx-form (36 damage taken) - attacked Merle (rolls yet to be seen) and then moved in Aulderoot's direction

15 Aulderoot - cast faerie fire, but the spell slid away from the strange avatar did not take hold

10 Merle - walloped the sphinx-form for 11 damage, but must now contend with strong jets of air blasting back at him

10 Merry -

6 Poppy -

Merry hurries after Merle but tries to keep to the shadows. Having retreated a few feet earlier (15ft), he finds himself unable to catch up completely and draws a dagger from his belt and hurls it at the sphinx (from 20ft distance). Then, he sidesteps when the Sphinx is distracted and tries to meld with the shadows. 

Action: Dagger ranged attack from invisible, hit 13,12 for 15 piercing damage
Bonus: Hide 17
Move: Follow 25ft and sidestep 5ft

13 unfortunately doesn't hit, Merry's dagger spins away on strange and unexpectedly shifting air currents and clatters somewhere at the further half of the room

Round 2

16 Sphinx-form (36 damage taken) - attacked Merle (rolls yet to be seen) and then moved in Aulderoot's direction

15 Aulderoot - cast faerie fire, but the spell slid away from the strange avatar did not take hold

10 Merle - walloped the sphinx-form for 11 damage, but must now contend with strong jets of air blasting back at him

10 Merry - missed with a dagger throw, but is still avoiding the sphinx's attention

6 Poppy -

Seeing his dagger being deflected, Merry grimaces but makes a mental note to where it landed to pick it up later (I removed one dagger).

Merle Dex ST: 22

Merle adroitly avoids the brunt of these blasts and takes half of 6 damage

so 1 damage, nice

Poppy can finish up this round

Seeing one attempt at Faerie Fire that failed to take hold, Poppy tries casting it too (DC13 dex save)

sphinx dex save 16

This time the faerie fire takes hold and the steel blue-gray form of the sphinx begins to glow with eerie light. The avatar tosses its head about as though irritated, though it makes no cry or roar, only a hissing sound as air continues to leak out from the cracks in its form. With more powerful gusts of air in the room, it moves laterally around Merle, apparently to line him up with Poppy, and then gives a great exhale of air from its mouth, like a voiceless roar. Hot air blasts out in a powerful spray, hitting you like a solid wall. 

Merle and Poppy, please make DC14 constitution saves and each take 6 damage and be knocked down for a failure. (Half damage on a save and not knocked down)

Round 3

16 Sphinx-form (36 damage taken, affected with faerie fire) - attacking Merle and Poppy with a blast of air

15 Aulderoot - 

10 Merle - 

10 Merry - 

6 Poppy -

Merle Con ST: 18

The air blows into Merle and knocks him a bit off balance but he's able to catch himself with his staff and stand firm.

Merle took 4 damage and it's everyone's turn for the new round

The eerie glow outlining the sphinx highlights a narrow seam in its flank, and Merry darts forward to exploit it. His whip snaps across the creature’s hindquarters with a sharp crack, the barbed lash digging into the glowing hide and widening one of the fissures that hisses hot wind. As the avatar twists in pain, he pivots toward the nearest stretch of shadow by the corridor mouth, meaning to vanish from sight—but a stray shard of shattered stone rolls beneath his boot. The slip sends a faint clatter echoing across the chamber, betraying his position before the darkness can swallow him.

Attack: hit 20,14 for 6 (whip) and 9 (sneak) damage.
Bonus: Hide with Stealth check 8 vs DC 15 (natural 1)

Aulderoot focuses inward drawing on a strange reflexive connection (false life) bolstering his bodily health (10 temp hp).

Merry, that hiss of hot wind slices towards you like a focused beam. Make a dexterity saving throw!

Round 3

16 Sphinx-form (51 damage taken, affected with faerie fire) - attacked Merle and Poppy with a blast of air

15 Aulderoot - bolstered his HP with false life spell

10 Merle - 

10 Merry - dealt 15 damage but must dodge a blast of air and also had a small mishap trying to hide

6 Poppy -

Merle tries to keep pushing the tempo in response to the sphinx and continues to attack.

Attack: 16 to hit, for 9 magical bludgeoning damage.

BA: Flurry of Blows

Attack1: 19 to hit, for 5 damage 

Attack2: 14 to hit, for 4 damage

Merle hammers against the creature, widening cracks and fissures while also subjecting himself to new blasts of dangerously focused air. Dexterity saving throw, please!

Round 3

16 Sphinx-form (65 damage taken, affected with faerie fire) - attacked Merle and Poppy with a blast of air

15 Aulderoot - bolstered his HP with false life spell

10 Merle - dealt 14 damage but must dodge a blast of air (please make a dex saving throw)

10 Merry - dealt 15 damage but must dodge a blast of air and also had a small mishap trying to hide (please make a dex saving throw)

6 Poppy -

Merry feels the air around him coil like a striking serpent. With reflexes honed on knife-edge battlefields he dives sideways, cloak snapping as he twists trying to put the corridor’s corner between himself and the searing gust. (Dexterity save 15)