STABmons
Each type combination has at least one very viable Pokemon and a few less viable/gimmicky options. Ironically (?) the two most viable threats are actually rivals in STABmons:
Scizor, a major setup threat and
Quagsire, one of the best answers to physical setup.
Scizor & Mega Scizor - Both of these are huge offensive threats in STABmons, more so the mega forme than its base, but either one should be taken into consideration when building a team. Bug/Steel isn't a great offensive combination, oddly enough. In fact, it fails to hit a lot of major threats for SE or neutral damage (Heatran, Thundurus, Landorus, Gyarados, Charizard, Aegislash, Talonflame, Rotom, etc) and relies on coverage from Superpower or Knock Off to KO them. But this offensive combination is not what makes Scizor so great; it's the
defensive combination that makes it such an offensive threat. Did I just blow your mind?
Since Bug/Steel is only weak to Fire and has important resistances, Scizor can come in on things like Kyurem, Aerodactyl (after a kill), Meloetta, Lati@s (lacking HP Fire), or Tyranitar and proceed to force them out and set up. It can also set up on defensive variants of Landorus-T, a very common Pokemon, since Earthquake doesn't hit hard enough and Scizor can Roost in between Shift Gear. For this reason Scizor often packs a defensive investment and Roost since it can guarantee living a few hits before retaliating at +1/+2 (Shift Gear) or +2 (Swords Dance). 150 base Attack is no slouch uninvested either, and with Technician it can still pack a punch if it needs to attack prior to setting up.
Quagsire - Meet the bane of most physical attacker's lives. Unaware is a great ability to have in a metagame where setup is king. However, it's not just the ability that makes Quagsire so stellar. Like Scizor, Quagsire has only one weakness: Grass. Though also like Scizor, it is a x4 weakness. Even so, Water and Ground give Quagsire a nice spectrum of type combinations it walls simply because they can't hit it for SE damage. 95/85 defensive bulk is not that great, but it's often enough to stomach a hit on the switch-in, Protect to gain Leftovers health, and then hit Recover to build its way back up to near-full health.
Don't think Quagsire is a sitting duck because it relies on Recover to check setup! It also carries Scald most the time, a move nearly every Physical attacker loathes due to the burn chance. Plus, should an attacker stay in and foolishly think they can wear down Quagsire through sheer willpower, they'll be met with a Toxic, or if the Quagsire player is feeling ballsy, it might start throwing out Spikes on your side of the field.
Overall both types are known for their defensive capabilities in STABmons. Scizor takes advantage of this combo to turn itself into an offensive threat thanks to its many opportunities to setup while Quagsire uses its typing to wall a lot of attackers and slowly wear them down.