When used against the Abyssal Sire, Shadow Rush has a 25% chance of disorienting it for the first phase of the fight.
When used against The Leviathan, Shadow Rush (as with all shadow spells) will stun the boss and trigger an end to it's usual attack sequence, allowing the player to attack from behind The Leviathan for a critical hit, causing one of two special attacks to be launched at the player.
Damage
Calculator
module = Magic damage calculator
form=MagicDamageCalc
result=MagicDamageResults
name =
param = spell|Spell|Shadow Rush|hidden|Shadow Rush
param = magicStrength|Visible % Magic strength|0|number|-80-100
param = specialModifier|Special modifiers|None|select|None,Slayer helmet (i),Salve amulet (i),Salve amulet (ei),Amulet of avarice (Revenants)|Amulet of avarice (Revenants)=haveForinthrySurge
param = haveForinthrySurge|Have Forinthry Surge|false|check|||Forinthry Surge is a buff acquired by defeating the Revenant maledictus while wearing an Amulet of avarice
param = weapon|Weapon effect|None|select|None,Thammaron's sceptre (Wilderness),Accursed sceptre (Wilderness),Dragon hunter wand
autosubmit = disabled