Let's be honest here - while Bastiodon has high defenses, his typing is crap. Weak to many common moves, and it's too slow to really do anything other than come in on a status Pokemon, and magic coat stuff or set up rocks.
Bastiodon @ Leftovers
EVs: 248 HP / 8 Def / 252 SpD
- Stealth Rock
- Magic Coat
NU (never used) tier, so that should be a little hint as to its viability in competitive.