How do you change Giratina`s forme in ORAS?

Question

I want the reverse-world form of giratina so I can actually use it in battles, since right now Its' movepool is crap and It's in overworld form. `Nuff said.

Answer 1

Griseuous Orb

Ou need to find this item which is found on Route 130 .
You'll need Dive and the Item Finder.

See this Video for more help

Answer 2

You need the Griseous orb like always the orb is located is
On route 130 Underwater it is also hidden so happy hunting