Mr. Fantastic vs. Juggernaut
No games. Juggernaut can't hurt Mr. Fantastic. Giving that kind of freedom and his Fantastic intellect, I think Reed is the one to Stop Juggernaut. I think he can invent something that could destroy Cain, like I think in my other thread that Forge too could do the same.
It's no more unrealistic that Reed should come prepared than it is that Juggernaut should wear his helmet to a fight.