Against teemo, At level 6, Teemo’s pressure increases thanks to his Ultimate t giving him extra damage and the ability to place Mushrooms t all around the map. 

The more ability haste Teemo buys, the more Shrooms t he can place around on the map. Try to take unorthodox pathing to prevent walking through them.

Nashor’s Tooth is a core item for Teemo. It gives him lots of additional stats- which makes him more of a threat. Against teemo, At level 6, Teemo's pressure increases thanks to its Ultimate t giving it additional damage and the possibility to place mushrooms t all around the map. The more haste Teemo buys, the more it can place mushrooms t around the map. Try to take an unorthodox path to prevent walking through them. Nashors Dent is a central element for Teemo. It gives it a lot of additional statistics- which makes it more of a threat.