I haven't really tried this out too much but I think it's liable.
Steelix w/ Leftovers or Life Orb
Brave Nature (+Attack -Speed)
EV's: 252 ATK/150 SpD/106 HP
Recommended IV's: 0 Speed
Recommended in Doubles or Triples
Gyro Ball - Power increases with how much slower the user is compared to the Pokemon it's fighting. (With an added STAB bonus)
Earthquake - High Power and works as coverage and a counter for fire types. (Also an added STAB Bonus)
Thunder Fang/Ice Fang - Ice Fang works as coverage and counters ground types while Thunder Fang is coverage and a counter for water types, use whichever works for you.
Curse/Rock Slide/Stone Edge/Stealth Rock Curse boosts attack and defense while lowering speed, which is what this moveset needs. Stone Edge has a high power and has a higher chance of a critical hit, with a downside of a lower reliability. Rock Slide has a lower power but a higher reliability, with a chance to flinch. Stealth Rock is also an option, annoying your opponent with instant damage the moment they send in a Pokemon.
Alongside a teammate with Trick Room, this guy can shine, sweeping through a team with his varied moveset.