Teemo's Blinding Dart (Q)
I think it would suit Teemo's play style and theme if his Blinding Dart worked the same as Quinn's Blinding Assault - having the Nearsight effect. Teemo's main problem is that he lacks a good escape and gap closing ability. His Move Quick is lackluster, unlike an instant gap closing ability. It's not good enough to dodge skillshots or to get in a fight. And his strength in his Q is that it allows him to fight against auto attacking champions only, but when it comes to skill(shot)-reliant champions, he doesn't stand a chance.
Teemo's auto attack range is quite short, which means he can't get close to a range enemy champions like Syndra, Xerath, Annie, without taking a skillshot/stun to the face. The only way Teemo could stand to fight a 1v1 against a range mage is if they step on a shroom and take damage before the fight or if Teemo builds tanky. Otherwise, he would be bursted the moment he enters their range. Imagine an enemy Syndra afflicted by Nearsight, Teemo would be able to get close to Syndra and not worry about her skillshots. It's the same with assassins like Zed, get in his range and you`re dead. But if Teemo can guarantee a blind he can get in, auto atk, get out. And let's face it, his shrooms cannot be actively used in a fight. Too predictable and situational, but if the enemy is blinded, it would allow for some play potential.
Anyway, I don't wanna write too long, but I really think the Nearsight effect would cover Teemo's main problem (sadly, bouncing shroom is fun and just fun) and make him viable not just in top lane but middle, against other mages/assassins, or even as a support.