Gragas can be played as a DPS or a Tank, I prefer to play him as a Tank due to his Drunken Rage's damage reduction and his initiating power. I've won and lost several games with this build, so don't expect to be godly with it or anything, and it does take a bit of practice but the concept is easy enough. Give it a chance in game before you vote, please.

Pros
- Great damage reduction when fully stacked with Leviathan
- Loads of health early game
- Great damage with Body Slam, and can body slam over almost any wall
- Good initiating
Cons
- Slow
- Ultimate is difficult to master
- No source of ranged damage, this build is for tank, not for barrel rolling, he's not Star Fox

I go with Attack Speed marks for better farming with your Drunken Rage, Armor seals, Magic Resist glyphs, and Health quintessences are pretty self explanatory. You're free to switch out the marks or quintessences if something like movement speed quintessences etc suit you better.

Standard tanking masteries with a point in Offense for the improved exhaust and some in utility for some regeneration, improved ghost, and experience gain.

Start out with a Ruby Crystal and as soon as you get to 800 gold, go back immediately to get your Leviathan. Your power lies in when it's fully stacked, so try not to die, and try to kill often. After this, we go for a standard Mercury's Treads for the magic resist and reduced CC, but boots are very situational, so choose whichever the situation calls for. This goes for building order as well, if they're heavy ability power, go for a Force of Nature first, or if they're heavy attack damage, go for Thornmail then Warmogs. The 6th item can be anything from a Frozen Heart to a Abyssal Scepter, really. Whatever you want to fill it with. I suggest Sunfire Cape, for the increased armor and seeing as how you'll be up close and personal with Body Slam, why not emanate fire from your swollen alcohol filled belly. Also makes farming a breeze.

We'll talk first about his passive. This is a great passive seeing as you should have a lot of health at all times. The passive allows you to regenerate health equal to about 2% of your maximum health. His barrel roll won't be gotten until level 13, and even then it shouldn't be used often until it's ranked up almost fully. This is because the benefits from Drunken Rage and Body Slam are more important early game then Barrel Roll. Sort of juggle the two skills a bit, seeing as the Body Slam damage increase is nice, but the Drunken Rage's attack damage increase (that makes Body Slam hit harder) is also nice, as well as the damage reduction. Speaking a bit more on these two skills, you should always have your Drunken Rage on. It massively increases your attack damage, makes your Body Slam hit harder, you get mana, the passive allows you to regenerate health, and you take less damage. What's not to like? His ultimate is a little tricky, it does some decent damage and pushes all enemies away from the center, this can be hard to aim seeing as while it's moving, if they even move a little slightly, the entire gank can be ruined, seeing as they'll be pushed away. Or even worse, you can try to push someone away from a teammate in danger, and end up pushing them even closer to the teammate. Always aim as much above them as you can, so even if they move up a bit, they'll still be pushed back. This can make for some easy kills early game, just ultimate them into turret range and slow them with Exhaust or Body Slam. I have a funny story about a match I once played. I was diving an Evelynn, and got her down to about 100 health before she stealthed. In a fit of rage, I threw my ultimate down directly ontop of me, completely forgetting that it's a very large AoE. I scored the kill, and Body Slammed my way away before dancing happily.

Always have your Drunken Rage on before initiating. That's the golden rule. You should Body Slam into them, and exhaust and ignite, etc. Try to keep auto-attacking him, seeing as Drunken Rage gives you massive increased damage, and if they get too far away, ultimate them back into your range for the finishing blow.

Farming is relatively easy with Gragas, with Attack Speed marks, and your Drunken Rage's increased attack damage. Just run up and when they have about 100 HP left, smack 'em with your head (atleast that's what the attack animation seems to look like). Even better, if you have a crowd of low HP minions, drink some, then Body Slam into the center. Easy mode.

You're a tank, so you should be initiating. Refer to the Initiating chapter if you're not sure how to. Try to ultimate enemies away from teammates about to die, or ultimate the dying ones back into the teamfight. If things get a bit heavy, ghost and Body Slam away. Remember, you shouldn't be getting too many kills, you're a tank, but you should be getting atleast a few. For instance, I just played a game before writing this guide and they surrendered, me being 4/1/10.

All in all, Gragas can be a pretty legit high HP/Armor/Magic Resist tank with some great damage reduction, while still dishing out a fair amount of damage. He's got a good escape tactic, but that doesn't mean he isn't slow, so watch out. He can chase quite nicely, and his ultimate can be one annoying skill. Not exactly game changing, but team-fight changing. Thanks for reading.