Pro Tip For You Mentalists!

When having a dummy inside a sealed envelope that leads to a headline prediction, at least have a fake prediction inside. If you do any publicity it could happen that the authorities that you hand the envelope to are means spirited and open up the envelope in your absence.

If they do, better have a headline written on the paper inside. You can claim afterwards that because they made it public what was inside the headline was changed, as the future was altered.