[9.1] Cernunnos, The Horned Support

Because who doesn't want to be a really annoying, permaslowing, rooting, boar-polymorphing hunter support? Just tell your teammates that you're actually playing Cern support so they don't mistake you trolling and just stealing the carry role.
Also remember that this build is extremely casual.

You should always use your Shifter of Seasons Winter Chill stance to maximize the slow from your basic attacks coupled with the passive of Frostbound Hammer. Try to make someone susceptible to being killed with the combination of your basic attack slows, your Bramble Blast's root and your ultimate - The Wild Hunt. Although it should mainly be saved for peeling diving enemies from your carries, it can of course be also used for initiation. Later in the game when you have more cooldown reduction you can use your ult more freely, but of course not unwisely.

With itemization, you should always be looking to build according to the match, except for the first three core items. Only exception to that is if you're losing early/midgame fights because of enemy teams healing, in which case you should get anti-heal before Frostbound Hammer). With the last three items, you're looking to get lots of aura - to compensate for the fact that you're playing a hunter support - and cooldown reduction as humanly possible while counterbuilding.
You can get to 40% CDR, but 20%-30% CDR is usually a pretty normal amount you can get if you also focus on counterbuilding for example anti-heal.
Mix and match with the items like putting together a puzzle.

These items are usually fitted in the fourth and fifth item slot.

Solid stats and a good passive, gets your team moving faster and gives mana back. Can't really go wrong with this item, especially when it also gives you some attack speed to play around with (while you have stacks on it).

If your team benefits from more attack speed and enemies don't really have healing, get Shogun's Kusari instead of the previous two. You can also get this if you like being "selfish" (it's an aura item) and want to have more attack speed.

You need to build anti-heal? Get Pestilence instead of the previous ones. If you don't like them healing at all, don't start doing any mental gymnastics and just get Pestilence, it's a good item.

If you're really scared of their magical damage, get this item if you're not impressed by the previous items.

These items are usually fitted in the fourth and fifth item slot.

Same story as with Pestilence. If you need to build anti-heal, get Contagion instead of Sovereignty. Can easily replace Sovereignty if you don't want them healing at all.

Good aura to have for your team, pretty self-explanatory.

Nice item for you to pick up if they have lots of physical damage in the form of basic attacks.

These items are usually fitted in the fifth and sixth item slot.

Not even that situational, with the addition of the new relic upgrades, this item is a very solid choice to get those strong relics back up faster.

Build if enemy team has multiple autoattackers. Simple. Witchblade also has some cooldown reduction to help with trying to max the CDR cap.

If you don't really need more of only physical or only magical defense, build this. It has cooldown reduction and both physical and magical defense. You don't really need to get Mantle of Discord because of our playstyle. It also has a steeper price, so just build Spirit Robe.

Pridwen has the same idea as Spirit Robe, get it when you don't really need more of either protection type. Also serves a purpose in maxing the CDR cap.

This build is an extremely casual one, and shouldn't be compared to a real support, they will always be better than this. The biggest reason you'd want to play Cernunnos support is the enemies' messages in lobby chat after the match saying "hoooly your build is annoying cern".