Yes, I know. The Health bar is on everyone's profile. I'll be working on that to get it off! But in the meantime, just check Mysterious's Profile for now and see how far his health is. If you keep your mouse over the bar for a few seconds, it will show the exact percent of where he is at.
EDIT: Or I may just use it for everyone and when he attacks someone, it takes down your health. That's what I'll most likely do! Good Luck to everyone! I hope you all will beat him and stay safe!