I play Yi extremely squishy but absolutley outrageously dangerouse up close. The items are expensive but paid for by soloing a lane near a turret and jungling. Buy the items bit by bit.

I am only a level 17 (in a 2 weeks) I have not noticed a difference when I use runes and not. I just looked up the ones that look like they woudl benifit my build for Yi.

I go almost all dmg with Yi. I ussualy run with the tank or range until I can buy teh dmg items...then teh fun starts.

Buy the recomended items bit by bit and start with the trinity because it has all the components that work for Yi.

a lot of newer Yi's think that meditate is useless but it great when you are about dead near a turret and have team coming.

Pros:
kills in seconds
very mobil
high KD great at jungling and lvling much faster than the others\

Cons:
does not fix the squishy yi problem
prone to ganks (they will focus on you)
without ult crowd controled hardcore

DO IT!!! ALOT