2 slows, 2 stuns, a knockup, a shield, % health damage, a revenge ult, and scaling tankiness? An engage and a disengage, peel for days, and high mobility? Why not Sion support?

E, E, E, E, E, E (enemy is below 25% health) walk up to them with shield on, hold Q until stun. W to detonate shield. Carry picks up the kill. Repeat.

Someone is coming to gank? Hold Q. Cancel gank.

Enemy is low and camped behind tower? Start jogging. Big hugs.

Someone's on my carry? Hold Q. Cancel carry aggro.

They're still chasing? E. Get off my carry.

Well I burned all my CC... Exhaust. I lied.

Exhaust wore off? My E is off cooldown again. Slow. Nyahahaha.

My team needs to engage! Time to start jogging. Big hugs.

My team needs to disengage... Time to start jogging. Big hugs.

Basically chuck minions at everyone. You'll pop relic shield with it and you'll scale your W health automatically. Every time you land an E, it's a huge slow and a ton of damage. And it costs basically no mana. Get them low, walk up to em, stun em, pop your shield, and let your carry figure the rest out. Sion support does NOT take a lot of brain power. I'm certain they'll nerf it to death soon.

Focus on poking down the enemy ADC with your E. If you have stacks on Relic/Targons/FOTM, try and hit them AND the enemy minion wave. Don't forget to send a minion flying if you have stacks and your ADC gets into them fisty-cuffs. It could heal them enough to win a duel.

You should do enough poke damage to keep a good amount of pressure off your ADC. Ward your bushes and keep your Q off cooldown as much as possible to stop ganks.

Harass as much as humanly possible. Once you get Catalyst, mana shouldn't be much of an issue. Grab glacial shroud early if you're having mana problems or if you feel like you need earlier CDR.

If you end up somehow playing on the backfoot, just keep minions flying and you should be able to hold off for a gank. If a gank comes pre 6, try and hit the enemy with a minion and a Q to set the jungler up. If it's post 6, go for ult, Q, and a minion as they run away (or just your shockwave.) Farm when you have chances to - it makes you tankier.

You are now your team's initiator. You're tanky, mobile, and have a ton of CC. Use this to zone other lanes when you have a moment to do so. Get wards out. Contest ward placement if possible. Mid game Support Sion is nearly impossible to kill.

If you get caught anywhere, just try and stagger/chain your CC as best you can. You can escape most situations. Try to pull the enemy towards your team so that they aren't dealing with JUST you. Never move far away enough from your team to where you can't bait a fight back to them. Sion is an amazing carrot on a stick. Farm when you have chances to - it makes you tankier.

You have max CDR. Use it to ult whenever you can catch a cluster of enemies off guard. Chain your CC to try and cause as much disruption as possible. Tank as much as you can. Peel for your carries. Do tank stuff. Ult is both your engage and disengage. Farm when you have chances to - it makes you tankier.

I plan on adding some alternate build paths as I tinker around with them. I just started playing this consistently about 2 weeks ago. I'm pretty convinced that it needs a hell of a nerf.

Questions, comments, concerns below.
-Riftborne