Zac is the newest champion at the moment and I have played a couple round with it. First I tought Zac sucks but then I found a build wich matches Zacs needs.
DISCLAIMER : I have not played so much with Zac that I would know wich Masteries or Runes you should pick.

When playing Zac you should focus training W skill first to max. Its good at farming and it does good damage. After that you should train Q and then E. Example : W,Q,E,W,W,R,W,Q,W,Q,R,Q,Q,E,E,R,E,E.
REMEMBER to collect the blobs that fall off of you when doing an ablity if youre not in danger.
If you are about to die and you have your passive recharged you should flash to near friends or friendly turrets so the enemy cant destroy the blobs.

Zac needs some hp so he would not die because of his own abilities. Also he needs much ability power so he would not have to waste all his hp for killing.
A great example of items would be : 5x Health Potion > Hunters Machete > Spirit Stone > Boots of Speed > Haunting Guise > Spirit Visage > Mercury's Treads > Liandry's Torment > Abyssal Scepter > Sunfire Cape

Zac is good at farming. You should use your abilities (Q,W) to last hit minions.

Zac is great in Team Fights. When teamfight starts you should use your abilities (Q,W,E) to get the enemy low on hp and then use our ulti and pick up the kills. If someone is running use your Slingshot (E) ability to catch the runner and use Q to slow the runner.

Pros :
- Great at ganking
- Good passive
- Fun to play

Cons :
- Hard to learn
- Goo