This build makes Master Yi a super strong ADC. (There are errors on the stats sheet for movement speed and crit - movement speed should be 391 and crit chance should be 100%.) Crit chance gets to 100% because of 25% from Infinity Edge, 60% from the two Phantom Dancers, and 15% from the Youmuu's Ghostblade. This means you are guaranteed to crit, which means your attacks are twice as strong. Thanks to the infinity edge, your attacks are 2.5 times as strong. The Last Whisper, Infinity Edge, Youmuu's Ghostblade, and The Bloodthirster give 210 attack in total. Your basic attacks become incredibly powerful and can kill champions at full health in a few hits. The Bloodthirster's 12% life steal heals a lot because of all the damage. I recommend getting an Avarice Blade right after the Last Whisper to help with gold generation and crit chance before crit chance is maxed (Avarice Blade gives 2 gold every minion/monster kill, 3 gold every ten seconds, and 10% crit chance. Also, conveniently, it can be built into a Ghostblade later.) Some other nice things from the build are the armor penetration from the Last Whisper and the Ghostblade, 10% cooldown reduction from the Ghostblade, 10% more movement speed from the Phantom Dancers, and 100% more attack speed from the Phantom Dancers. This build is even better after the Master Yi 2013 rework because now Alpha Strike is based on physical damage and can crit, so Alpha Strike will be way stronger. Use Alpha Strike to close gaps and hit four enemies at once, wuju style to boost attack, and basic attacks to finish them off (take advantage of Double Strike if you can).

Of course, if you like this item build, don't be afraid to use it on other melee ADCs like Tryndamere.