I love champions who can gank in new and interesting ways. Zac is certainly new and interesting (and all kinds of silly), but is he worth dropping the money or IP on? Let’s find out!
The coolest thing about Zac is (outside of his aesthetics) his massive jungle sustain; if you stay on top of getting the goo from your passive, you’re probably not gonna have too hard of a time in the jungle. He also clears reasonably quickly, thanks to his low-cooldown AoE spell in the form of Unstable Matter (W). His ganks are also really powerful… assuming you can land his knockback and slow (E and Q respectively), which I’m really godawful at, so don’t take any ganking advice from me. His passive also lets him dive quite nicely, but… Well, that doesn’t help if you forget that it exists. My apologies to every laner whose gank I’ve botched because I forgot that I’ve got a less-amazing version of Eggnivia.
In terms of teamfights, Zac seems really slow to get going. I’d argue that early-game is his worst enemy; without a lot of HP and resistances, you’re going to get crushed pretty quickly. He also doesn’t put out a huge lot of damage, so you need to bet on initiating with your slingshot or ultimate, then having someone else clean up. Don’t be afraid to die, either; that passive really helps if someone decides to tunnel-vision your bloblets. Also, if you can poke people down with Q or W, make sure to pick up your dropped goo so you don’t get half-dead when the actual fight starts.
Regarding how to build him: Forget about a lot of the AP items early on. Zac definitely needs tankiness. While I’m sure he could do a ton of damage if you built right, it’s not really worth it if you go in, get your passive popped, and then die. He’s one of the few champions that I’d argue for Warmog’s Armor as a super early item.
All in all, I’ve had a pretty good time with Zac, but… He’s definitely not for everyone. If you’re really looking for another jungler (in case the others aren’t quite doing it for ya), then by all means grab him. Otherwise, wait until free week to give him a shot. Anyway, as always thanks for reading and have a good’un.