I already made one of these but it has disappeared. When playing on a server my CPU usage goes from 30% to 70% every few seconds causing me to freeze. I have tried reinstalling the pixelmon version and updating to the latest optifine but nothing has worked. Please help

It depends on a lot of things. First off, check this link, and ensure you are following all tips and guidelines for optimal performance. http://pixelmonmod.com/wiki/index.php?t ... ory_issues
Secondly, how much RAM are you assigning? 3GB is personally better, so try that. Then again, if you computer has a max of 4GB, then it is not a good idea to assign that much. Lastly, check your system updates - do you need to update a graphic driver? It will boil down to your computer's performance.

There are also server-issues that can cause this, so either join the Pixelmon Discord, or ask to the server you are playing on. That will help us, better help you.