Sion is a very simple champion to use, there are no high skill combos that take forever to learn or hard to hit skill shots. Sion is Sion. He is the ultimate cheese god. You should always cheese the other team lvl1. As a toplaner you have 3 options. 1 you steal their red/blue tp into lane. 2 you hide in the top middle bush and q wave and your laner. 3 You hide in the bush that the laner will come though after leashing his jungler. With glacial augment you can get him down to 50% in just a few hits.
As support you can invade if you have a lot of cc on your team to help with your q. If your jungler starts red, you and your adc always should go into the bush that they come from for cheese. It usually ends up with adc dead or all sums blown.
With the lethality build you should spend a lot of time in bushes waiting for unsuspecting squishes to come and get one shoted.
YOU CAN STEAL BARON
I bet you didn't know that your q reaches the baron hitbox if you charge up your q from the blastcone side. If you go ad sion your q can deal over 1k damage.
When splitpushing, you get collapsed on a lot. You can ult out in the direction of their base. ULT INTO THEIR BASE! You can turn around for easy escape.