Glacial Augment acts as a replacement to Frozen Mallet allowing you to abuse your range in lane and build into more offensive items. By building BotRK you also gain an additional AoE slow.
Biscuits are a great means of sustain allowing you to save money on potions and invest it into you damage items to further push a lead.
The money saved from having to buy potions, thanks to Biscuit Delivery, offsets the the Lending Fee of Future's Market so you can snowball any game to victory.
Approach Velocity synergizes extremely well with Glacial Augment and Teemo's [R] allowing you to chase any enemy to their death.
The beauty of Absolute Focus on Teemo is that you're often dealing damage to champions when you are full health and even in base, thanks to any mushrooms you have spread across the map. Teemo is likely one of the biggest abusers of the Absolute Focus rune.
Scorch is a fantastic rune for abusing and poking in lane. Teemo can easily proc this une on cooldown thanks to the long range of his [Q].