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.
It's a damage heavy build early that transitions into health/dmg items to maximize the effective health of true grit stacks. The frozen mallet slows them down making it extremely easy to put down aa and build stacks quickly while making sure people can't escape from you. Once you have steraks and stacks with the lifesteal and deaths dance passive you're very tanky and slippery allowing you to put down decent damage non stop. Very strong against assassin teams.