The Phoenix is the alternate form of Emily Hayes.
After Emily lost control of the stone, it transformed her into a giant firebird. Emily soon destroyed the underwater fortress and flies off.
Flight- With wings comprised of flames, she is seen to be able to fly.
Extremely hot temperature- The fire that engulfs her body seemingly cannot be extinguished, even within the depths of the ocean.
Fire breath- The Phoenix can release a pillar of fire from her beak, similar to a dragon. She is seen using this as she attempts to incinerate Trellis as he is escaping, but he blocks the attack with a shield.
- With Emily only being in this form at the end of Firelight, she may have more untapped abilities.
- With Trellis being tasked with returning her to her normal form, we have yet to see how her transformation with be reversed.
- Emily's transformation is likely symbolism of her anger over her father's death consuming her like fire.