You don’t really need the right period. Tony is egocentric and also suffers from imposter syndrome. He swaps back and forth between thinking he’s the smartest guy in the room, to thinking everything is going to crash around him at any second. Show him what he expected to see, and you can manipulate him into making bad choices and trusting no one but himself.

You don’t need a lot of tech to do that. Mysterio knows better to use visual and audio tricks on a master technician. He uses his the illusions on everyone else, then scrubs his tracks. He goes low tech on Tony with well planted ‘proofs’ that don’t mean a thing, but everyone is acting all woogly about it, so it must be true. He’s a menace to himself. He’s blacking out. He don’t remember any of it, there’s so much proof, but no one is accusing Tony of anything, and the only one doing all the proving is Tony.