Handle SPELL_AURA_ADD_TARGET_TRIGGER at cast function.
TYPO AT: Remove MOVEFLAG_ROOT from movementFlagsMask = MovementFlags.
Apply every aura stack to dispel list:

More Aura Charges cause a higher steal or dispel chance for this spell.
Example: 5 Stacks Winter Chill + 1 Polymorph : 5/(5+1) for winterchill, 1/(5+1) for Polymorph