Giratina is the sheer definition of nightmare fuel. Imagine if you took a dragon, and fused it with the most darkened, horrifying visions of Giygas and the Null Void itself. It still doesn't even come close to this terrifying being. Giratina, as the draconian incarnation of Satan, is indescribably powerful, rivaling old Bob Saget and even Thanos. It can banish you to its home, the Distortion World, or even wipe you from existence with one Shadow Ball. However, it is not this immense strength that makes Giratina special, no, what REALLY makes it stand out is its ability to travel through the UnOmniverse at WILL. Wherever it wants to go, it goes there, no questions asked. It is also the only creature immune to the Null Void, being made of it. Not even the boundary-breaking Indoraptor has touched the Null Void unharmed, yet Giratina defies this. However, Giratina is not evil, it merely watches over the dead souls that threaten reality. One of Giratina's most famous souls was Cyber-Dee, who later got released.
Outside the Pokeverse
In all reality, Giratina is only this absurdly powerful in the Pokeverse. Outside, it is only as powerful as Giygas. I still wouldn't recommend messing with it, lest you want your organs ruptured.