Grim Idle (Xbox One)

Pretty straightforward. Just keep playing through the game and walking through portals until you get to the tenth zone, at which point the achievement will pop. As you progress, the enemies have more and more hit points, so take longer to kill. If you find the going gets too slow, you could perform the ritual to get some black wax to spend on upgrades (though this resets you back to the first zone) or open a chest or two to hopefully get a better weapon (you can get free ones from completing in-game objectives). Remember to be constantly leveling up your weapons to give you more damage as you go through the game. You should easily get this within an hour.