You can activate the effect of “Charm of Shabti” during the Damage Step.
“Charm of Shabti” is like a reverse-“Kuriboh”: you take damage from the attack as normal, but your monster is unharmed.
Netrep Rulings:
“Charm of Shabti” can be discarded from the hand in response to a face-down Gravekeeper monster being flipped up by an attack if that Gravekeeper monster would be destroyed by an attack.