All though Discord is probably one of my favorite characters from MLP, and even cartoons, Bill Cipher trumps him in basically every way. It's really the fact that if Bill ended up in the real world against Discord, he could crush him with a single blow, as he did with Time Baby (A god of time, who is supposedly unstoppable). And to top it off, if Bill was in the real world, he would be invincible to almost anything. To sum it up, Bill Cipher is a being that is more insane and chaotic than Discord.