ljfa

Well the more memory you give it the more is it going to use. Also, keep in mind that your operating system, other programs and Java itself also need memory. So giving it more than 4GB is probably not a good idea. On another note, it would help if you give us the crash report. We don't have crystal balls here, sorry

Can you post which mods you are using? Else we can just grope in the dark. I was gonna say Blood Magic, but then it would not just be the overworld.