Why Yi is still viable. Yi is great because he forces the enemy team to break off 1 or 2 of there front liners to stop his back line rampage. Also he can be super tanky and deal huge damage if built properly to the situation you are in. this guide will help you to build him properly as well as why you aren't supposed to go 20 and 4 or what ever as Yi (you can but i don't recommend it).

Always be ready to adapt your build to what you see. If you see Garen is going warden mail first change from going strait to botrk to you cleaver, or a Vampiric and a Brutalizer. Now this is learned over time but this will hopefully help. also remember to always buy wards. lol is not a game of who has more kills it's about who has smarter plays and you will almost always make better decisions if you are warded.

Master Yi is still a great pick for ranked. This is because he is great at applying pressure and being that annoyance there team has to deal with. First if you are dominating lane expect to be camped, but use this to your TEAMS advantage. If there jungle is top that means there are only 3 vs. your 4 on the bottom half of the map and your team can use this to get a dragon. you want to split push until mid to late game and try to keep 2 or 3 top at all times. This creates great openings all over the map. But you must be aware of when your team needs you to join in fights. in fights your job is to jump on there back line. You alone, if you haven't been shut down, can kill 1 or 2 of there carry's if there front line doesn't break off your's to help there back. This allows for your front line to get them grouped and stay on there back and relives pressure from your back line. If there front line doesn't help there back just kill them all and move on to win.

Pros

Very high ad early game.
Strong mid game pressure.
Can transition into many kinds of Tank/DPS late game.
Easy to kill tanks top.
Good at split pushing.
Will destroy carries.

Cons

Very squishy if shut down.
Very loved by jungle gank.
Hard to come back late game.
If enemy's are every good they will collapse on you before you get that much damage off.

that last one is a pro and a con because if they are focusing you they aren't focusing you carries.

Last hit? not much here but try to keep the enemy top from getting cs.

Overall Master Yi is a Great top lane pick and is easy to learn. a great pick for and new or veteran solo Q player.