Master Yi is up there with the best characters for dominion because he is agile and very simple to use if you learn him you should be able to get first in dominion almost every game with this build.

Master Yi has a very simple page all you need is your basic Armour penetration & Attack speed.

I use the basic 21 0 9 AD masteries

The only problems you will really encounter is more AD characters like Vayne and Kow'maw and Twitch because they have stacking passives

all you have to do to be a good Yi is to play smart and know your limits (but you realy have none)