This build is designed for Teemo to attack quickly while getting that extra ability power for the extra damage from your Q, E, and R abilities.

The mastery tree goes 21-9-0 for the extra offensive ability power masteries and extra defensive masteries. If you choose to modify this go right ahead, not like I'm gonna stop you from doing so.

I find Teleport is very useful when the enemy team is pushing a turret and no one is nearby, or if they need help. Surge is useful when you're pushing a turret and don't have quite as much time as you would like to destroy the turret. Surge is also nice if you need to kill someone quick, then use your W ability to escape before an enemy champion shows up for a gank. Ignite is not a recommended spell for Teemo as his attacks are already poisonous.

I choose to get my Q, W, and E abilities before getting my ultimate (MUSHROOMS!), but you don't have to if you don't want to. If you want to get your Q first in case of early game fights, go ahead, but I find the poison helps at times as it can scare the enemy, making them think they'll die (if hit enough) or if you chase them and they go behind the turret, the poison has a chance of killing them or making them recall.

The runes chosen help with magic penetration as well as armor penetration and attack damage, whilst still getting the extra defense Teemo requires to avoid dying as easily. If you want to change to runes to be more offensive (more AD or AP) feel free to try, I just find this works really well when I play.

If you're being killed a lot, I suggest switching boots to Mercury's Treads if you're taking too much magic damage, or Ninja Tabi if you're taking too much physical damage. If you find there's too much ability power and not enough attack damage, go ahead and change Malady for The Black Cleaver or something.

Teemo's mushrooms allow him to slow down an enemy champion while still damaging him. This can be very effective when being chased and the enemy runs into a mushroom, as well as when you are chasing down an enemy. I suggest placing mushrooms in bushes, in the river (as to avoid being ganked), and definitely out of the way of enemy minions. Placing mushrooms by Baron is a good idea as you will see if the enemy team has gone to kill him, in which case you can set up a gank or steal Baron from them. Mushrooms last up to 10 minutes (unless stepped on by an enemy unit) so placing them by Baron just before Baron spawns or by neutral monsters in the jungle is a good way to inform you on where the enemy could be/what they are up to.