http://na.leagueoflegends.com/champions

Any one of those with only a slow for CC. There's quite a fair amount.

Assuming Solo Queue Normals where your team doesn't stick with you.

Only having a slow doesn't help much against a yi, his ult makes him immune to any slows and he runs ridiculously fast.
You either need really high burst or a few stuns in your team to take him down easily.

Ninja Tabi. Each hit does 10% less.

This is why you run Exhaust.

lol slow...yi...hilarious
you need to stun him then kill him, slow before his ult you can usually kill him to crush his progression, but it doesnt work after lvl 6, never will