Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Sion gains damage from his ability and is a natural born tank with his passive making him an excellent fighter, you can easily stun someone, run up and get 1-2 hits at lvl 1 and then get out of there as the enemy runs away. After you get malady and Starks, you can easily take down a dragon or any squishy champion. Dont bother with boots unless you need them for defending against stuns like another Sion or Morgana etc.
You can regain health pretty fast even at low levels with just the vampiric sceptre, so if you still have 1/3 of your health and the enemy runs away or has less than you, just farm minions until you can fight again.