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.
The Mpen runes on Garen is probably controversial, however, hear me out. Judgement may be a large source of damage, but how frustrating isn't it when you ulti someone and they get away with a sliver of health because they have magic resist.
It also helps boost the sunfire capes and people generally stack more magic resist than armor, hurting our magic dps more than our physical dps.