>>57768629Those are their Original forms, they use them to navigate their own dimensions as Giratina does. As to why they look more like Arceus there is a good reason to it. Dialga and Palkia are parts of Arceus. Giratina is not, he was born as the other side of the DNA of the universe, mere consequence of the universe itself existing, acting like a balance, so says Cyrus. So Giratina's Origin form further gets away from looking like Arceus, while the other two who are part of Arceus, get closer to his shape.
