I know how to fix Teemo
To clarify, I know how to make Teemo more bearable for his opponent in lane without decreasing Teemo's overall effectiveness as a champion. The problem with Teemo is that playing the champion well is synonymous with ruining your opponent's enjoyment. Deny them minions, poke them literally ANY moment they are not under their tower, etc.
To address this, I propose a single change to Teemo, specifically to his blinding dart, which will greatly reduce his toxicity as a champion (pun intended) while having only a minimal impact on his ability to contribute to his team.
The change is as follows:
#Enemies hit by blinding dart miss their attacks against all units champions.
Suppose Teemo is fighting an enemy champion. He blinds the enemy champ. Since Teemo is a champion, he is still able to avoid the enemy's attacks and win the fight.
Suppose Teemo is in a team fight and he blinds the enemy adc. The enemy adc misses its attacks against Teemo and his teammates because they are champions. Again, no change.
Suppose Teemo is jungling. He uses his blinding dart on a jungle monster to avoid dying. The monster misses its attacks against Teemo because he is a champion. Still same as before.
Suppose Teemo is laning against a champion who is trying to farm. He blinds the enemy champion, but the enemy champion is still able to last hit minions because the blind only stops the target from hitting champions, and his opponent is attempting to hit minions. Teemo can still deal a ton of damage with his attacks and dart and win trades, but he cannot stop his opponent from farming outright.
In summary, I believe that the above change to Teemo's blinding dart will have a tremendous impact on his opponent's quality of life without taking away the raw power that Teemo players enjoy.