Sion vs Yas, how does Sion win this?
I played sion supp one time vs a yasuo adc and it was practically impossible to land abilities on him. What should I do in this matchup?
I played sion supp one time vs a yasuo adc and it was practically impossible to land abilities on him. What should I do in this matchup?
if you can't beat a yas adc there are bigger problems on your hands.
Stop trying to rely on skills to hit him. Auto attack him, and use Q to kill any nearby minions. This will drop the minions from your lane on him, and he won't have anyone to E to besides you. If he wastes his E on you, he will have to manually walk the rest of the fight. Then you can stun, etc.
You can also just engage with your Ult, stun him, and then Q while he's stunned. He also can't block your W.
Likely, the biggest reason you're losing with Sion is that you're trying to build armor. Sion's strength is in "Survival" not actually tankiness.
A build that might win you vs Yas:

I know it sounds nuts, but items that decrease damage taken from basics or engaged targets are better than going pure armor vs someone like Yasuo. This build will put him on grievous wounds, reduce his attack speed, both reduce his basic attacks and any damage done by him after you've hit him, and it gives you 60% crit rate. And, if Yas barely gets away and you have nearby minions, you can use the Hydra to tap him from a range.
Personally, i think if you die to Yas as Sion, you have a tendency to stand still. Orb as if you weren't a giant tank. Sion's much stronger when he keeps moving than when he face tanks.
Thanks for the tips.
Hide in the bush and charge your knockup. He can't see it if he doesn't have vision of you in the bush (get a sweeper or control ward to be sure). That'd be my idea.
Otherwise just poke the support instead? You'll outscale anyways, Yasuo is not a good ADC. Your ADC should be attacking him from range while you stand there to deny Yasuo engaging on him.
Curl up into a fetal position and focus on the tiles of your floor... or the carpet.
Buy an early bramble vest or really any armor item. Sunfire and thotnmail are best
Yas is a terrible match up for sion, so good luck.
rush is your friend, also
and 
If you are sion support though go
because you want to be safe but also want to protect your adc.