I was in a game where somebody called mid and I was told to jungle. This guy changed to jungle Yi at the last second. I ended up being support Xin Zhao because out support was Annie and she could mid.

I was like 8/0/17 at the end of the game. (Even without exhaust)

Pros
Strong Tank
Knockup, Slow, and Ultimate Knockback
Good Initiation with Lunge
Goood Peel with knockup and slow

Cons
Little Damage
Can be Kited
Can be hard to get off the 3 attacks needed for knockup. (Ashe would be good partner to help keep them from escaping to ensure you get the 3 attacks. This or get attack speed early. Maybe aim for Zephyr or Trinity as 6th item.)

Core is the basic.
Armor
Sunfire just to have any sort of reason for enemies to avoid standing near you.

Sunfire can be replaced with Frozen Heart or Omen in many situations

Magic Resist
Visage is the go to. It is good just for stats. If you end up with Rageblade or something, then the heal bonus can be helpful, but that takes a bit of attack speed and AP (via W passive)

The rest are common core support items.


Boots Enchant! - I would go for Furor, but if you get pushed back into the base go for Homegaurd. Furor helps you chase.

Frozen Mallet- This is to prevent enemy escapes, but I was fine without this thanks to the lunge slow and knock-up. (It is rare a support will get full build anyways)

The health bonus gives even more heal to the Face of the Mountain heal, so this is why i picked it. Ideal because it has health and utility.

2nd Bet - Warmog's - This is great because you should be able to get out of fights easy enough if you are low. This allows you to sustain and do other things, place wards, etc. without having to back thanks to the passive.

Thornmail - Counter to fed auto-attack based champs.

Banshee's - Counter to fed casters. (Mildly). Also more to counter CC initiation.

ZZ'Rot - This is great for pushing, with the high health it makes this very strong. Hide it in the closest bush to the tower you are pushing. Just check the range on the item and make sure that there is enough for the minion to hit the tower. (Give plenty of bonus room, because if the minion gets slowed down by creep collision it will probably not get to the tower.)

Tip; If you can get Zz'rot early, it is a good investment. The minions can earn you a lot of gold as you get money when they CS a minion, and it can put extra threat on a lane, especially if you are actively pushing the lane.

Omen- This is to prevent escapes, and slow enemies that chase you. The health is nice.

Frozen Heart- This is a good counter to fed enemy ADC and auto-based champs, as they will likely not be attacking you.

The stats that really help support xin are basically only attack speed, while AP can give a small amount of sustain in the lane.

Attack speed means you can get your Q off more reliably.


Guin-Soo's Rageblade- This is a great item because the AP gives you bonus heal. It is easy to keep it at full stacks when laning. It is also quite cheap compared to others. The proc at 50% health wouldn't be too impactful (with low damage output on both ends), but the bonus attack speed, AP, and damage all help your threat levels.

Trinity- An all around good item. The con is that it is quite expensive.


Maw- This is a good item if you could use more Magic Resist

If you get Zephyr, sell your merc treads and get swiftness or ninja tabi. Zephyr gives you more chase and flee ability.

Ruined King is not great because lifesteal is not impactful without much damage, and the passive is not impactful without a lot of attack speed. The active effect is nice.

People love to take these items as a support, but i tend not to because I am a low quality player who does not use active effects reliably.

Zeke's- This is a great item if your ADC is doing big things. This is like a 7th item for them basically. The stats aren't amazing, but they can do a bit.

Locket - This would be my go-to support 6th item. The health bonus is good for the Face of the Mountain, the MR aura is nice, and the active is a quality shield.

Crucible - I would only take this if there is a quality CC that practically gives the enemy team kills. (I think this works on Fizz ult, Malz ult, Ashe ult, and things like that.)

W and E are more important to a suport than Q. You get the knock up from just one point in Q, any more points are just damage and cooldown. W and E help you secure the knockup and ensure that it happens.

I would run
9x Atk Speed (red)
9x Scaling Armor (Yellow)
9x Scaling CDR (Blue)
3x Movement (Quint)

Atk speed for getting off Q
CDR for more ulti and ability uptime
Armor because tank
Movement for posisioning and escape.

Stay behind the creeps and out of harass range.

Try to initiate when one of your opponents is out of position or comes in to try to harass.

Watch out for enemy ganks and try to counter with the E->Q->W combo

Use R if you can get in front of an enemy to knock them back into your squad during a team fight.

Use the relic shield charges. Easy money and heals your buddy.

Learn how to ward.

Upgrade your trinket.

You should be in front of your ADC if they are trying to run (you are melee and they are ranged), if there is an enemy in front of you try to peel them off by using the combo. R can knockback any additional enemies if you have it available.

Don't be reckless or overagressive. Opportune strikes hurt more than reckless ones, and recklessness can often get you killed.

Be a boss and CS when you are alone in lane, this gives you that income. Just dont steal CS from your ADC. (It should be hard to do if you have no shield charges seeing as you do little damage)

Maybe not as important for this guy, but i always turn off auto attack, especially when playing a support. This keeps you from messing up the CS of your ADC, and it helps me to CS when i ADC because i can time it much better.