The original Mysterio is Quentin Beck (the failed SFX dude) and he literally has no natural powers. He’s a master hypnotist, special effects designer, and he can make a mean robot. He’s also got some skills as a chemist as well, but he’s basically a big-time illusionist who uses his tricks to make everyone think he’s more powerful than he actually is. Here’s the thing though: historically, Beck can throw down because the man knows how to fight.
His gauntlets just aren’t there to play up his magician persona, they’re functional as well and are outfitted with a bunch of different gases. Think Scarecrow from Batman — his gasses can knock people unconscious, poison them, dull Spiderman’s “Spidey Sense”, disintegrate his webbing, and make people hallucinate, which assist with his illusions. Many of his tricks and mind games are projected from the weird helmet he wears, along with holographic projectors he’s created. His suit’s been known to pack electric coils that shock those who get near him, and powerful laser shooters to fry dudes he’s fighting. He’s like a David Copperfield/Iron Man hybrid.