Does tons of damage early use it to get kills. Later on it will allow you to run since you are magic immune while spinning.
One level gives enough heal for a while, use this to heal up the team.
Not needed in lane so get this later once team fights start happening.
This can kill heroes solo very well. Use it to start team fights or to kill heroes that you meet 1v1.
Starting Items
Heals up after getting harassed.
Helps you last hit and farm jungle.
Early Game
Every hero needs boots to run faster.
Core Items
Allows you to move through units while spinning as well as giving you some more damage.
Allows you to hit a lot harder.
A good DPS item and makes you run faster.
Late Game
Illusions give you more damage and add some confusion.
Gives tons of DPS and evasion.
Situational
Get this if you will be farming and pushing a lot.
Get this if getting stunned is a problem.
Get this if you need a stun.
This will make you attack very fast and push well.
Other Items
Gives you some more early damage.
Good heal when you are low.
Makes you take less damage from harass.
Gives you a good aura and lifesteal.
Get this if your team has another carry and you need more magic damage.
