A prediction, displayed in big printed letters on a huge billboard, or displayed on a photograph days before the performance?
An impossible effect? The mentalist asks a spectator to name any freely chosen piece of information (a playing card, a number, a word, the name of a person etc). This exact piece of information is then shown to be on the internet, not only far away and with no possibilities of multiple outs, on top of that it turns out that this exact prediction had been sitting there, in advance, for days already.
An impossible principle? Imagine there was a method for thumbwriting that made it possible not only to do the secret writing on a 'billet' that is not in the performer's hands, but that’s in the spectator's view the entire time; - and to actually do the secret writing even AFTER the spectator has already unfolded the billet, while they are reading its content. All this without the magician even having to come close to the spectator at any time!
Welcome to the 21st century.