Gold Experience Requiem
Gold Experience Requiem A.k.a. Requiem or GER is a stand power featured in Part V: Golden Wind. It is the second stand of Giorno Giovanna and the evolved form of Gold Experience created by piercing Gold Experience's body with the stand-creating Arrow. When Requiem first appears it wears the arrow on its forehead, but moments later we see it fall to the ground.
Powers
Nullification of Action and Effect: Gold Experience Requiem's ability is to turn anything, including his opponent's attack and willpower, back to the state of "zero". Hence, it is near invincible, as all "supposed" actions created by an opponent would have been reset (back to point zero). If the opponent is killed by the stand itself, then they will also continuously experience death, as they will die but repeatedly return to point "zero". It is mentioned by Giorno himself that he is unsure of the exact workings and limits of Requiem's powers. Requiem also appears to have a consciousness of its own that is unknown to Giorno.
In other words, Requiem has the opposite effect of King Crimson; while King Crimson erases the "cause" while keeping the "effect" (i.e time where a bullet would hit him is erased, causing the bullet to warp past him), Requiem keeps the "cause" but erases the "effect", thus causing endless scenarios where actions and initiatives are started, but the effects of such does not occur (i.e Diavolo's incomplete cycles of deaths, upon dying by Requiem's Blazing Fists, he would then experience the knife of a heroin addict, an autopsy gone wrong, being hit by a car, and so on for eternity.)
This ability turns Giorno essentially untouchable by anything that would try to hurt him and is perhaps the strongest defense ever in the series.
Original Ability
It is often disputed whether Giorno retained his original life giving abilities after evolving into Gold Experience Requiem. After fusing with the arrow, Giorno breaks a column and a piece of it turns into a scorpion that then attacks Diavolo, the turning of a piece of stone into a living creature, so it is very likely he still has all of his original stand's abilities.