It is a dagger that allows Cataldi to reflect damage received at someone else.
About 50 cm (20 in) in length, the Stand is bound to a straight double-edged Napoleonic-era dagger (around the end of the 18th century and the beginning of the 19th century.) The dagger itself features a decorative hilt and a rusted blade, but shines like a mirror when the Stand is active.
Despite being bound to a dagger, Dolly Dagger acts more like a passive ability.
Its damage reflection is a redoubtable power as it will automatically damage the attacker and makes Vittorio naturally more resilient in combat. However, it backfires against Stands with multiple bodies, as they can withstand the damage better than Vittorio himself.
Partial Damage Reflection: Whenever the user takes damage, 70% of that damage is transferred to whatever is reflected on the blade of the dagger, while the user still receives the remaining 30%. Gunshot wounds and even viral infections can be transferred.
The Stand can not only reflect attacks from others but damaging one's self can also direct the damage to whoever is reflected in the blade. The damage that is received is in the same location of where the damage was dealt. The damage that is reflected is not what was dealt physically, but rather "the level of damage" that was received, i.e If a man in a suit of armor attacked, and his attack was reflected, the amount of reflected damage he would receive would be irrelevant to how well his armor can defend against physical attacks.