Zac is an exotic pick for support yes, but it can be very useful one. He is well known for his CC capabilities and we are gonna exploit them as a support. The enemy won't be able to do much in a fight when they are stuned for the first 2-3 seconds of it. Zac is strong here because of his high engaging skills and his decent disengaging mechanics as well.

The most effective way to use this Zac as support is to have good communication with your adc, so he can know when you will engage and who you both should be focusing. As well as using skills in good synergy.

First minutes will seem like a weaknes to Zac, but that's not entirely true. Yes, you will not be as tanky and won't have a lot of range in your E, but you still have pretty good cc power.

First minutes
If you reach level 2 before your enemies, you will be wanting to engage. First, use your E and land it whoever is more easy, then use your q and ideally slam the both champs into eachother, if you cant aa both, just hit a minion. If you see that you are doing much damage to the objective, throw exhaust on him, he will most likely flash or heal away from you.

If you have early lane priority, you might want to try and get in sync with your jungler and catch enemy jungler when doing the south Scuttle, as it might be an easy kill.
Lane Strategy
There are two main tactics to use in phase lane. You will want to try and poke the enemy landing your Q in medium range to one them, then slamming him into a minnion and using your e in a quick short way to cc him and deal him damage, the rest of the damage can be made by your adc.
The other tactic, and the most importat one is moving through the bushes. This will put important pressure on them, as they will back off preventing you from landing an E on them. If they do the other way and keep farming, engage the adc if he is in range of your E. Having good vision is very important for you,try to clear the wards of the lane bushes as soon as they put them.
Getting ganked is a thing Zac Support is very good at. Just engage, keep them cc'd and try to push them towards your turret with your ult.

ENEMIES SHOVING INTO TOWER
This is an awesome feature of zac that you and your adc MUST exploit. This is obvious since Zac and his jungler nature permit him to go in and out of lanes easily. This tactic is done by wating for enemies to shove into your tower and CCing them under it to then keep them as long as possible in towers range. You must keep unseen by them before doing the trick, make sure of this by keeping vision control near tribush area. This is done more easily when you are in the red team because of the closed tribush area. Ashe and Varus are perfect synergies for this tactic. They both can R an enemy while he is hitting the tower and keeping him cc'd . You have also to use your R to push im further into turret after the cc Chain, you can use flash for this.

Roaming
Whenever your adc has backed or your lane is pushed deep, try to roam to mid and help your teammate just as you would do with Zac jungle. Just be careful on not getting too behind in expierience in lane. You should also be aware if your jungler needs help with enemies getting into his jungle.

Zac will also be decently handling 1v1 against certain enemies in mid and late game. This depends on how well you are doing. When 1v1-ing make sure to collect all of your blobs so you can heal, blobs after Spirit Visage will heal you a lot.
In this stage of the game, Zac should be used just as you would use him in mid-game if you went jungle, just remember to have good vision control of the map so you can ambush anemies and prevent ambushes from them.
You can decide if going for a more engage oriented playstile or for a more peeling-for-carrys attitude as you see how the match develops.

I want to thank you for reading my guide, this is my first guide ever and it had to be made for my beloved Zac. People will maybe think you are inting but if you follow this simple tips, you will prove them wrong. I wish you good luck and happy matches, KEEP THE CC COMING!!!