Here is the full list of all 34 Omensight achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Unlock all other trophies
Jump on the head of all your companions
Break a barrel thrown by a Shark while it's in the air, by throwing a barrel at it
Imprison Voden
Launch 4 Phantom Blasts while inside Delay of Fate's sphere
Execute two Lethal Flurries in a row
Use Lethal Flurry 20 times
Throw a bomb towards a column while inside Delay of Fate's sphere
Unlock the Kladen Seal
Defeat Ludomir in battle
Unlock the last Omensight
Unlock Vera's Seal
Kill 100 Rodentian fighters
Unlock all Harbinger's Blade upgrades
Unlock your second Omensight
Unlock all Harbinger's Aegis upgrades
Use Phantom Grasp 50 times
Use Phantom Dash 30 times
Use Companion ability 50 times
Kill 100 Pygarian soldiers
Unlock the Rodentian Seal
Defeat Indrik in battle
Kill 100 Ciphers
Use Delay of Fate 20 times
Defeat Draga in battle
Use Phantom Blast 20 times
Kill a surrendering enemy
Launch a Phantom Blast on an enemy thrown with Phantom Grasp, while inside Delay of Fates' sphere
Unlock your first Omensight
Kill four enemies with the same column
Unlock all bonuses at the end of a day
Defeat Ratika in battle
Unlock the Pygarian Seal
Witness Voden's appearance for the first time.