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.
This is a great build for gragas with a balance of damage and ability power making all his moves viable. Drinking before every battle is very important for the damage reduction and his attack damage, but if you have nashors tooth you can keep up drunken 24/7. I try to hit single targets with body slam in battle because it does tons of damage instead of spreading it around as well as slowing targets that get hit by it.
After the patch came out gragas has been a very powerful hero if you know how to play him right with this build. I play him constantly and carry teams with this build. Good luck to everyone.