In addition to your neat shirt/hoodie, you'll also obtain the rare 'Rainbow Sash', an in-game visual commodity only made available for special events. Rather than the standard sash awarded to the Pixelmon supporters that have donated to us in the past, the Rainbow Sash cycles through the color spectrum, showing yourself off as a very special Pixelmon trainer.
To gain this Rainbow Sash, simply forward your purchase receipt with your PixelmonMod.com username, and your Minecraft Username* onto firstname.lastname@example.org - Your sash will be activated after the campaign has ended.
* Your Minecraft Username is only necessary if you have not linked your Minecraft account to your Pixelmon website account.
Note the Rainbow Sash is available only on Pixelmon Mod versions 3.5.0+, and 4.0.4+