Alright, I know I bashed AP Yi the other day, then one person, not so calmly might I add, was quick to defend him and state how good he is. In my defense, the reason I was bashing him was because of the people I went against, who often did rather poorly when trying to build him and ultimately ended up just feeding the whole game. Whether it was their fault or the team they were with, who knows. I just know from my experience going against him, I thought he sucked. Though recently I decided to give him a go with some friends, we initially did it to just troll during the match, but the results did surprise me a bit.
So obviously AP Yi is a different creature than the standard AD Yi that I am more accustomed to. You're heavily reliant on your partners for most of the match, as you mainly use just two skills in a fight. If they have stunners or something that can interrupt your channel for meditation, that can just ruin your day, unless your team works with you to initiate in those scenarios. Generally though I found him to be quite fun and quite amusing to play. Pretty much the role I kept taking on was the person who ran up, Alpha Striked to harass, and if my team felt up to it, either tank them with Meditate or just get the heck out of there and repeat.
The bad thing though, is that you're totally relying on two skills, with only one of them doing damage, so compared to other AP characters, you can get outclassed in damage fairly easy. On the flip side, with meditate converting your AP with a 400% turnover, your survivability is rather high unless they do really high burst damage to you. I remember in one of the games I used him in, that heal actually helped us win, as they would try to focus me as I healed over 300 hp/s. This also allowed me to tank the towers for my team to do a quick push to win. In other matches this even allowed me to tank a Tryndamere while he popped up his ult and started wailing at me desperate to grab a kill. So yea, situations like that will actually get my friends and I to laugh while it happens.
So yea, I am a bit converted on the whole AP Yi idea, just took actually trying it instead of judging by the players that ultimately failed at that approach. It is fun, but not for all situations, and you get heals that can get downright insane. Though it isn't a build I would try without at least one of my friends to lane and compliment the character with.