Teemo shrooms need a model update, asap. He needs a texture rebalance like a lot of champs have been getting lately.
As far as Nerf/Buff goes, Teemo is actually in a nice place right now. Everyone will say they hate Teemo, but he's really not OP at all. His poison will wreck you if you try to trade with him, but if he's building for damage then you can just kick him in the face and he's dead. He has low range for a ranged champion, and blind doesn't do jack. His blind is useless 90% of the time, and immensely OP 10% of the time, they need to redo that mechanic of his.
If he's nerfed, he'll become unusable, but if he's buffed he'll become the demon everyone thinks he already is. Basically they should just give him a texture rebalance and maybe fiddle with his Q mechanics (I'd like to see it become a single target skillshot fear or "hallucinate").