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Also, wanted to ask if this has happened before with previous versions of pixelmon?
If something like this happens with regular minecraft (single player)?
Could you try playing in an online server if you haven't already and see if the problems still exist
By default the pixelmon launcher (to my knowledge, i dont use it) uses 1GB or ram only like the old minecraft launcher (using the new launcher will auto allocate 2GB now).
To change your allocated ram. Start up your launcher and click the gear icon in the top right hand corner. A new tab will appear with some options. The 2nd slider down is the allocated ram and will probably be at 1024mb (1gb). Change it to 2048mb which is enough unless you are running some seriously heavy mods.
Considering that the game runs fine in multi player and crashes in single player, Im wondering if it's a problem with loading and generating worlds. Moe suggests it could be related to bad world names.
Uninstall pixelmon, delete the pixelmon folder located in C:\Users\Ss\AppData\Roaming\ and redownload the pixelmon launcher. Deleting the folder should remove all worlds in case any is causing an issue.
Also, personally I don't have any fml logs in my minecraft folder (I don't use the launcher, but that shouldn't matter), I know my server has fml-server logs but don't have any client logs on my computer. fml logs should be located in your logs folder, along with the latest.log