Teemo is too powerful for how versatile he is. With his poison he can push lanes and farm better than just about every other hero, which leads to him having more money and experience than just about every other hero. He can harass and do huge amounts of damage mid-game one dart at a time followed by withdrawing from combat, forcing opponents to retreat for health while he continues to farm. His mushrooms planted in every ****ing patch of grass on the field make it next to impossible to flee from his team mates and move quick is just frustrating.