I kinda don't want Herobrine as the only villain. I think we should introduce Null, who's keeping Herobrine captive and the heroes help Herobrine escape, only to realise that he betrayed us. Then we could introduce Entity 303, who helps us defeat Herobrine. He doesn't betray us, but he is trying to turn us into glitches so he can rule the Minecraft realm, and then Steve (aka the first player) will help us defeat him. No betrayal there.
I mean, it doesn't matter if Herobrine is the only villain. I'm still in even if you don't use my idea.