I strongly suggest Cetitan.
Speed and raw strength are the only things that matter in casual playthroughs. Yes, Avalugg is an outstanding tank in terms of shrugging of physical attacks, he is horrendouly slow and has a worthless Sp. Def stat.
Cetitan has raw strength -- just like Avalugg -- and impressive bulk -- also like Avalugg. Despite his defenses, at least Cetitan's bulk goes into his HP, meaning he can survive a flamethrower... unlike Avalugg. Not to mention, Cetitan has better abilities. Sheer Force slapped onto a good moveset lets him destroy whoever crosses his path, and Thick Fat makes fire type moves of normal effectiveness. However, Slush Rush is where it's at. This guy really can sweep.
I AM NOT SAYING AVALUGG IS BAD, BUT CETITAN IS SIMPLY MORE EFFECTIVE.
With some simple Mirror Herb picnic stuff with Makuhita, you can access Belly Drum. After that, the rest is easy.
Cetitan @ Sitrus Berry
Ability: Slush Rush / Thick Fat
Tera Type: Ice
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
- Belly Drum
- Ice Spinner / Icicle Crash
- Earthquake
- Play Rough
Make sure to have a snow setter if you choose to run Slush Rush Cetitan.
If you still want to go with Avalugg, use this.
Avalugg @ Rocky Helmet
Ability: Own Tempo
Tera Type: Fighting
EVs: 252 HP / 252 Atk / 4 Def |OR| 4 HP / 252 Atk / 252 Def
Impish Nature
- Avalanche
- Iron Defense
- Body Press
- Heavy Slam