Here is the full list of all 21 Schein achievements.
First collectible found.
Defeated Zenel.
Kept the green light lit for 60 seconds.
Met the Irrlicht.
Walked left at the beginning.
Completed Schein.
Half of all collectibles found.
All collectibles found.
Defeated Sartasis.
Defeated Ermatu.
Caught a lantern mid-air 25 times.
Completed Schein with less than 100 deaths.
Completed Schein with less than 50 deaths.
Listened to the secret dialog.
Died in water 100 times.
Died in fire 100 times.
Died on spikes 100 times.
Ride platforms for a total of 5000 meters.
Kept the red light lit for 60 seconds.
Kept the blue light lit for 60 seconds.
Left the lantern behind.