Congrats on the pictures... One problem from me on them, they are mixed, from blurry to different sizes... Try and use PNG for your extension... Also, another thing that could help is decreasing from millions of colours down to say 255, just an example.
Now, I don't like the mixture of Gen3 tiles (is that?), with Gen4+ battle, it looks odd next to each other in the pictures.
Thanks for clearing up the gym thing too