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It can be presumed that Giratina's origin form is made of pure antimatter and it's regular form is regular matter to keep it's body from self-destructing, since Antimatter tends to annihilate when touching regular matter.
Doing some math, Giratina-Origin is 649997.9 (which will be rounded to 649998) grams of Antimatter which would result in producing 27923914.08 kilotons-equivalent of energy.
tl;dr don't give your giratina a griseous orb, he will level the entire region
