Ok, here's a thought for Zac...

You know how for Sion's W, every enemy killed gives him permanent bonus health?

You know how bonus health gives Vladimir bonus AP, and vice versa?

What if we gave Zac a passive on his W that for every so AP he has, he gains a certain % of bonus health regen?

Like, if we gave him a +1/2/3/4/5 (+1% AP) bonus health regen every 5 seconds.