Hello! I'm apaahlo, and I make off meta builds for champions I enjoy. for the past few months, I've been playing sion as an adc, and it's been incredible. before the duskblade nerfs, it got me a 85% winrate over the course of maybe 20 games, and after the nerfs I sit at a 70% winrate, which is higher than my winrate with him in other roles. I AM low elo, so maybe take this with a grain of salt.

Sion adc works well for a few reasons, I've found.
1: lots of cc
2: surprisingly high poke dmg
3: enemies struggle to plan vs it
4: high health in mid - late game
5: great waveclear
Yes these attributes all make it seem better in mid lane, but this lane choice is moreso just to abuse the constant 2v2 nature of the lane. He can struggle in solo lanes vs high poke, but that poke becomes less of a problem when you have another champ with you to help with it.

if your jungler starts botside, always leash until you see the buff dip into triple digits. as soon as that happens, run to lane because you will be able to charge a q just enough to get that 3 cs and prevent your opponent from shoving too quickly. if not leashing, try to cheese them out by sitting in a bush near their wave. if they have a hook support, sit in the river bush because you might get a sneaky kill. farm to level 3 and if you have advantage in levels at this point, go for the all in. use exhaust before you hit your e if you can because if you dont get both hit, your q can be harder to hit when they try to flash out. if they flash behind their wave, sit between their wave and them, to zone them out, and farm. if they flash sideways, keep the fight going and get your kill.

make sure your item spikes hit by going dirk first always. clear waves and push for their jungle camps and stop their jungler from hitting any kind of late game spike. play for your teamfights and remember, youre also an assassin. you have bulk, but you will be focused by their team, so play safe, even though its forgiving. bush cheese as much as you can, and hopefully you get all the objectives.