My name is Jason. I have played Master Yi since season 8. Although I have only been in gold, I understand the fundamentals of the champion and his kit. Although he is a more linear type of champion, I believe you are able to climb with any champion with the right mindset. Master Yi's biggest enemy is CC. If cc'd, he is easily shutdown and thus needs a tank or other cc to back him up in fights.

Why Lethal Tempo? I have tested a few different keystones, such as conq, lethal, and hail of blades. Hail of blades is best for burst builds that require max dmg in least amount of time, like lethality/crit builds. Most comps will have a tank, and although hail of blades can work against tanks, on-hit provides more synergy with items and more dmg when running keystones like conq and lethal.

Biggest misconception about league what to build on a champion. The question that people ask is, "What is the best build?" and they look up the "best build" for the champion that they want to play. There is a difference in "the best build" and "the most common build". Most of the time the "best build" will have a high winrate because players who use those items/runes happen to win games. Of course there are item and rune syngeries that work better than others, but always pick your items/runes based off the enemy team. If I know I am going to get cc'd frequently, I should have the rune: Legend (tenacity), or buy Merc Treads, etc. With experience, you won't need to lookup builds because items can be very situational, again, it all depends on the enemy comp.