Description: When I found out that this monster could learn Mirror Coat I was like YISSSSSSS! Suck it special attackers.
Basically you can tell from the choice of nature and EV spread that this set allows Avalugg to sponge any neutral physical attack, I'm not sure if he could sponge a Mega Mawile iron head, or powerful fighting moves though, thankfully sturdy ensures he will use a move.
-Mirror Coat is to stop special attackers cold, while hanging in there with sturdy (assuming you're at full health).
-Air Balloon is to support Rapid Spin. Although Avalugg doesn't care about sticky web, Spikes and Toxic Spikes will ruin sturdy, and being able to have a free switch in to predictable Earthquakes is a nice touch.
-Recover or Rest is down to personal preference (Chesto Berry if you're using rest).
-And the last slot is also down to personal preference. A powerful physical move such as Avalanche or Gyro Ball may be the best option, but Swagger seems like a cool idea since Avalugg will eat up but the most powerful physical attacks anyway, and the confusion, with a little luck, will allow him to recover any damage taken. It will also troll contrary Malamar, but I don't see the 'mon very often in online battles.
And lastly, if you still doubt Avalugg's defencive capability, you could give it one of those berry's that reduce super-effective damage, such as the Charti Berry (rock) and the Chople Berry (fighting). You could replace replace the healing move with swagger and keep the physical move if you feel the healing is unnecessary.
This is a good moveset for avalugg (Pokemon #713) with the sturdy ability/trait, a Impish nature, and equipped with Air Balloon submitted by Hoharvey. For use in competitive Pokemon battles featuring an Export option and breeding guide.