Well Metal Burst can be taken as an offensive move, saying as it allows him to take he hit (which he obviously can) and then kill the poke that hit him, as long as they're slower than Bastiodon (and with base 30 Speed and a -Speed nature, that's pretty much everything). I actually used Bastiodon in Gen 4 NU/UU for a time, and that bitch can take an Earthquake from an Adamant max attack Nidoking, as a sign of its sheer bulk.
Yeah. The only truly notable things that OHKO him are stuff like Rhyperior Earthquakes or HJK from Medicham and whatnot. He even gets Sturdy, which nets him even more assurance from moves like that. And then when his dream world ability gets released (soundproof for some reason), he will be one of the best specsmega answers in existence, because he would be immune to bug buzz, take next to nothing from air slash, and would only fear HP Ground.