252 HP, 6 Def, 252 Sp. Def
- Leech Life
- Bulk Up
- Focus Punch
I'll begin by saying something upfront: Bug/Fighting is a pretty bad STAB combination--offensively. That's because Bug and Fighting are both resisted by four different types. But on the other hand, the nature of this set does not need Bug/Fighting to be particularly good, and you don't need strong STAB coverage when you've got Focus Punch and Leech Life. To start, Substitute has naturally good synergy with both of them, and Bulk Up even more so. You're healing yourself with Leech Life on a set that does not naturally have enough room for good HP recovery. And a boosted Focus Punch from this thing, well, it kinda hits hard enough to turn a Dump Truck into garbage. You know, a 300 ton, 3,500 horsepower durable machine of stainless steel that deals with things far tougher than the average Pokemon. 2x resisting Focus Punch isn't going to help much because even then, Focus Punch still has a good 75 base power. Bulk Up makes it so that your opponent can't break the Substitutes you set up, and it has to be said that base 107 HP and 139 Defense are already naturally good. After +1 or +2 those subs are not going to break in one hit. And substitute means you can fire off Focus Punches willy-nilly without you needing to flinch; when your Sub doesn't break your opponent is going to have to eat another. Did I mention how Focus Punch 1-hit-KOs stuff and how Beast Boost makes everything worse? Yeah, that's the fun part.
Since you can't boost your Sp. Defense, investing in it is a good idea because otherwise Buzzwole is more easily sniped by special attackers. On a side note Buzzwole can make Substitutes that can't be broken by Seismic Toss or Night Shade. Although in case you haven't noticed, pretty much anything that's a wall is screwed by this, as long as, of course, they don't carry a flying or special move it's weak to, Roar, or Whirlwind