I am trying to make a block that helps players but hurts everything else. I have looked around and haven't found an answer to this and I am sure that someone else has com across this issue.

 

Here is a copy of the code: http://pastebin.com/xHNiyzuQ

And here is the copy of the crash that I get: http://pastebin.com/WvxhM3aw

 

This only happens if my block has an effect that is being applied to the mob. If there is not effect then it is ok.

 

Thoughts?

Well, the parameter if the method is of type Entity, yet you blindly cast to EntityLiving:

} else{
   ((EntityLiving)entity).attackEntityFrom(DamageSource.wither, 1.0F);
}

And, as you can see in the crash report, there are all sorts of other entities that might be colliding with the block:

java.lang.ClassCastException: net.minecraft.client.particle.EntityBreakingFX cannot be cast to net.minecraft.entity.EntityLiving

Always perform a type check (e.g. instanceof) before casting to a new type.

Thanks. I will make sure not to do that again. Great full for the help.