The first two bytes indicate what image data to use, while the next two bytes indicate the palette. The enumeration for this is the same as that of the 00 command- in order for an effect to work properly, the 00 command must have been called for both of these- otherwise the palette and/or image will not be loaded. While the existing animations appear to always have these be the same, they don't have to be- you can for instance give the Stun Spore seeds Fire Blast's palette this way. For some animations both of these are 00- I believe these are effects that don't use images, such as Earthquake's screen-shaking.
I'm not entirely sure what the rest of the bytes do, but it appears the two pointers after these values contains more image data (I think the dimensions and how it animates, respectively) while the rest of it has to do with how the effect plays out. I've fiddled with it a bit and done some interesting things like these:
Interesting, I have been editing moves myself and haven't come across this yet. Could you please clarify on this? I am slightly confused of what a 00 command is.
Also, not sure if this has been discovered, but if you wish to easily find the data for a move, find the animation pointer (I suggest using Gamer2020's PGE Attack Editor for it) and highlight the bytes of the animation until you reach the following bytes together:
08 00 XX 27
This string tells us that an animation has just ended and is moving onto a new on. Make sure to highlight everything up to the 08. DO NOT HIGHLIGHT THE 00 XX 27.
XX refers to, and my guess, the image data for the next animation.