Omnistrike

Omnistrike is a deadly phase where The Solemn One teleports to the middle and gains 90% damage reduction through a passive effect active while Omnistrike is charging called Shroud.

Possibly not accurate: Depending on the damage shades inflict on player's units, Omnistrike gets charged by a small percentile. Either this, or it gets charged gradually depending on how many shades are alive.

Shroud
Incoming damage reduced by 90% while shades are active.

Solemn Shades
Shades can take up to 12 attack instances or 1000 (2000 with 200%, and 1500 on Beyond, coming that with 200% mode would equal 3000) damage before being dispelled.

Omnistrike cont.
Omnistrike's statistics are:

Damage: 250 x Amount of Shades

Range: 99

Weapon Speed: 60

Inflicts damage to all heroes equal to 250 x Amount of surviving shades. etc.