Master Yi(eet) analysis
Do you want to climb elo, do you want to carry the whole game for only getting fed with 3 kills? Do you want to pester your enemy jungler (like seriously I deal with this all the time) then master yi is for you.
This champion has been around since day one of this darn game, and he is one of the highest picks in blind. Sure, he has high damage and mobility. The problem is with yi at the moment is that he carries a little too hard... Sure, cc'ing him can do the trick, but kind of hard since he can be immune to slows with his ult, and can be untargettable 30% of the time, making him the dodge-lord of the century. Then later in the game he can just get 3 kills and start hard carrying with massive damage and speed InNiCiAtE sAnIkK mOdE. I hate yi gameplay-wise in general, sure, but he is still a well designed, and fun champion to play. Another thing to note, it is soooo easy to get a penta off this guy... this champ was the reason how I got my only pentakill ever (but it was in bots when I was practicing him so doesn't really count).
Anyway enough of the chit-chat and get into the deep stuff. This multiscoped Samurai (idk) guy has a few things you need to keep in mind. One: Q to win. His q is his best tool for offense and defense, he becomes untargettable while hitting up to four target... but ends up on the first target and how does that work? I don't freaking know... but always max this. His w... let's be honest, it isn't THAT good... sure, it's pretty broken in urf considering you can spam this over, and over, and over..... but in a regular match it does heal you, but you should note you cannot move so your just left wide open for attacks. You mostly want to use this to hold off the opponent so you can get the cooldown of your q so you can outplay them. His e is... it's alright... You get free damage with it ready, and even more when activated, but none if its on cooldown, so you can figure out when to use this in a team fight, either stick with the damage you have, or having to quickly kill them faster with bigger damage, your choice. His ult is pretty BUUUULLLLLLLLL CRAP!!! He gains massive movement speed, and cannot be slowed. Considering cc is the only way to stomp this guy, him popping this ult will ruin it, unless if your champion has a stun. What's more, he has a passive with his ult that makes his cooldowns ridiculously shorter. This makes him the ultimate chasing tool to make jax blush, he cannot be stopped. His passive is pretty well with trading auto's early game, it's always a great help.
So is this champion OP? a little... because he is immune to slows with his ult which lasts quite a bit, and his damage is ridiculous. However he is still balanced in the spot that, it's either you flunk completely as him, or you hard carry your team as him, and usually I keep finding the people with that second option, be it my team or the enemy team. He has a few weaknesses, considering he has barely any way of defense besides his q, and his w just heals him, other than that he is pretty squish unless you build tank on him... if so why would you build tank on this guy.
He does have a few counters... Mainly champions with decent stuns, and also untargettability. Akali is one because of her shroud, Kayn because his shadow assassin form cheeses yi so hard, zed somewhat because of his ult, and so on. Another way to counter yi is not to build armor, he can eat through tanks faster than you think. Instead, either get a teamate to help you, bait him into a trap, or use stopwatch, since there is almost nothing you can do to his damage. However, you can also have a high damage assassin on your team, like shadow kayn, to tear him up.
Anyway, if your looking for a fun, basic but a still viable champ, yi is just the champion for you (even though I still hate fighting him).