User blog comment:TheAggravated/Yang Yin, Upholder Of Balance/@comment-1330314-20121130181746

The kit you gave Yang Yin makes him more of a carry than an assassin, since he'll be stacking AD and would be doing a lot of autoattack damage. You also have a few balance issues: his base stats are too high (health, health regen, energy regen, armor) and he scales Magic Resist, which he shouldn't unless you want to make him more tanky (which an assassin shouldn't be).

His passive's damage bonus is way too high, and still would be with even half the bonus. You may want to go with a more reasonable one like 10% extra damage when under 10% health or something (or, alternatively, slight extra damage when over 50% health and slight increase in armor and MR when under 50% health). Imagine a normal fight where after a while you'd get under half health and start mowing down everything in sight with free double damage, it could easily get you a pentakill with no great effort required.

I like the idea of an armor and MR drop on Balance Strike. Bring Balance, though, has too high a healing amount and doesn't fit an assassin kit at all. Think about Taric, for example, who's a tank and whose heal in the late game only covers around 10% of his health, or Tryndamere whose self-heal is even less powerful. Dark and Light sounds like a nice idea, though the cooldown's a little low for a dash that long-ranged.

Equilibrium sounds like a nice ult. Again, with your kit it's more of a carry ability (but nonetheless an amazing carry ability).

Overall, you've got a lot of nice ideas, though they don't look like they all belong on the same champion, let alone an assassin. Try saving the support abilities (Bring Balance and Dark and Light) for another champion while focusing on more burst-oriented (if you want him to be an assassin) or carry-oriented abilities for Yang Yin.