The new mastery system hates zilean.

I'm sorry, but it's true. Literally NONE of the keystones are even remotely good on him if you play him as a support (his primary role.)

Warlord's bloodlust? Gosh no Fervor of Battle? Not unless you're playing adc zilean (where you clock your opponents?) Deathfire touch? Only one spell works, and it's aoe, meaning that AT MAX you can proc it for it's full .2 ap ratio one time. And that's only if you go ap mid Stormraiders? Yeah no, chunking people for 30% hp isn't something easy to do on zil (especially not support) and he DEFINITELY doesn't need another speed boost. Thunderlords? Also no. Proccing it is impossible unless the enemy continually eats double bombs, and even then you have to throw in an auto for it to work. Windspeaker's Blessing? Nope. Zil doesn't have heals or shields. Grasp of the Undying? Nope. Zilean has one of the worst HP pools in the game, and he's ranged. Strength of the Aegis? Nope. Zilly isn't going to be killing minioins as a support. Bond of stone? Nope. You'd THINK this might actually be okay on zilean, because he can help support his adc, at least, but guess what? Every time the ADC takes damage, it considers you "in combat" for the sake of your passive, so if you use this, just say goodbye to your passive, because it's a sure bet that when you can level the adc, they'll take damage and throw it on a 10 second cooldown.

Literally none of them are even remotely good. I'm sure zil isn't the only champion in this boat, either.