Ahaa, the stock image came from this amazing fanart I saw on deviantart, and I rendered the image myself. The image had green light shading, and if you look closely you can see the green light reflecting off Giratina's face...but in that stock image, the green worked amazing with Giratina, but maybe the green I used was a little too bright? I guess I wanted it to contrast with Giratina's dark figure in the image.
Yeah you're right, I should darken the background a bit, but for a first attempt I reckon it turned out great