The "Blessing: Immune to Immobilization" only applies to the buff, and not the casting. The cast of this skill may be interrupted before the buff takes effect.
While this buff is in effect, you cannot be flinched, knocked down, pushed back, aircomboed, nor killed, and your attacks and skills will not be interrupted.
You still take full damage from enemy attacks.
Some attacks can ignore this buff.
If you are affected by a CHOKE debuff, you will still collapse if you reach 0HP.