The only reason i take upgraded smite and ghost are for other champions because i mainly use the same mastery set for most of my characters. Also Ghost and Master Yi's ultimate scale very well together for chasing and escaping so ghost is an easy alternative for clarity. The reason i use clarity is because im often using Alpha strike to farm minions and it has a large mana cost.

I take out the infinity edge that most people have in their yi build for another bloodthirster, it does insane damage and gives great lifesteal when it has full stacks, and the frozen mallet helps keep you alive and gives you even better chasing abilities due to its slow, PLUS you have 2 phantom dancers which gives you a very useful speed boost.

When being ganked with yi I ALWAYS stay to fight and almost always win ive gotten multiple quadra kills from playing yi 1v4 its actually crazy how beast he is. When Being ganked always use exhaust on the character thats dealing the most damage or the one with the most hp that way they arent bothing you while you killing the squishies in a 1v3,4 or 5 and make sure to use alpha strike SMART when in a battle, Don't use it to deal damage, use it to avoid damage because Nobody can hit you while your using the skill until you land. You simply target the squishies and exhaust the annoying characters while your life steal and ult keep you alive from crazy attack speed and use alpha strike to avoid damage.