I've seen a little talk of this around, but wasn't able to find a video (which may be due to my bad searching skills...) so I decided to make a quick one. Until an update comes out that allows us to more easily add skins to the custom trainers which were added in Pixelmon 3.0, I found this little workaround. I think it's pretty simple, and hopefully the short video below will explain everything you need to know!
(Note, this method doesn't work for servers unfortunately since this will only change the skins on your personal Minecraft/Pixelmon files.) That said, it's perfect for single player worlds or personal adventure map type things! Let me know if you have any questions, or any feedback! Hope you enjoy!
[youtube]https://www.youtube.com/watch?v=ZjfUJ2ZgGyw[/youtube]
If you're interested, I also have an Adventure series running on my channel that uses these custom trainers for Gym Leaders, etc. So check it out!
Thanks!
First Episode of my Pixelmon Adventure Series, with a custom map, custom trainers, and CustomNPCs is here: https://www.youtube.com/watch?v=BH-6Qx6OUM4