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