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.
At first u should start off with buying boots of speed and 2 healt potions, and try to stay together with someone. Mordekaiser isn't the best in the begining but once u start to level up the fun will begin. Then u should get sunfirecape followd by Force of nature, warmogs armor, Rylais Crystal scepter and finish with The blood thirster.
He is kinda hard to play with, but when u use him as a tank, it will be pretty easy.
Feel free to give some pointers :D