In Fact Sion is a slow but tanky bully on the map showing up suddenly with his ult giving massive cc and even after death a threatening opponent you should stay away from.

The Idea is to increase his Speed add up to his CDR and get him enough tankyness to herr*** survive and cc the enemy team. His bad points are the charge of his Q which is easy to dodge and the lack of speed in early game.

Sion can use his Q not just to herr*** and cc but also to zone out enemys to keep him at distance when playing top. When you gank a lane try to hit your E while you can predict his next movement then rush in and knock him up with a half charged q while charging you get your Shield with W and stay close to be able to activate it any time.

Use your Ultimate wisely its a strong tool to engage in TeamFights. If u use it start from within the lane or you will end up in a wall. When you connected to the enemy team place a short q instantly to slow there movement and focus someone out with your e who will die instantly after the team charges in. You can time your W while your running to burst out additional damage after landing.