Pixelmon keeps crashing in Minecraft?

I've installed Forge mod loader and then installed pixelmon as my only mod since i've reset my.minecraft folder just to make sure nothing goes wrong and now if i play on single player my client crashes maybe 20 seconds in after i walk break blocks collect apricots etc… And if i'm playing on a multiplayer server my client crashed 2 seconds in i don't know why can anyone help me and also i've heard mobs spawning under the ground in caves and i'm pretty they arent supposed to spawn in pixelmon i'm using fml installer 1.6.4 pixelmon version 2.5.7 and my minecraft is set to 1.6.4 any help? Btw if you don't know **** please don't answer…