I'm interested in finding out about customs so if anyone could help that'd be great!
How do I create customs?
How does the general system work?
How much does it cost to create them?
Any other important information?
Thank you!

Here's an answer I gave someone on the same subject a couple of weeks ago:

"When Krin releases a monthly avatar set, he also releases a .psd file with certain elements from the set that we can recolour (most often the helds, but wing and back items have been included in the past). You open this file in an image editing program and recolour the item how you'd like. Once you're happy with it, you save the file as a .png. Then, you message Krin with the .png and he deducts the amount of diamonds that the item would usually cost (between 200 and 300 diamonds usually), plus 100 diamonds, and sends you a copy of your custom avatar item. You can buy additional copies of your custom for 100 diamonds.

Here's an in-depth guide (with pictures) created by Flute ^.^

Enjoy!"

Basically, you have to wait for a monthly set to be released (there wasn't one for November, and there isn't one for December either, so the earliest possible next one is January). You can send in customs until the end of that month. After that, you cannot make new customs with those items, however any customs you have already created can be bought forever after for 100 diamonds each.

Hope that helps!

Thank you! ^.^