Here is the full list of all 8 Firebird - there are La Peri achievements.
Get backstage and find Iskender’s entrance with your flashlight.
Unlock all the achievements.
Discover all illustrations in the ancient book of La Péri.
Steal the petal from the air avatar.
Steal the petal from the water avatar.
Steal the petal from the earth avatar.
Renounce immortality and preserve the Péri’s dance.
Keep the flower for yourself and become immortal.