Runes make your early game damage crazy.

Mastery tree give you all the stats you'll need : Ability power,Magic penetration,Percents bonus damage,Movement speed

Items give you magic penetration ability power or in other words everything you need to buff your Q spell. And in bonus you have movement speed and 2 item actives for bonus damage in fight.

Summoner spells give you movement speed to catch up enemies and true damage for finishing low health champs or for reduce healing and when ignite is in cool down you get bonus attack damage and ability power.

Very bad farmer or probably the worst.

Late game could even 1 hit squishy enemies.

Pros
Early game nice damage
Late game Crazy damage
Difficult to catch

Cons
Easy disabled by any crowd control
Low health