Metagross @ Leftovers
Ability: Clear Body
EVs: 196 HP, 252 Atk, 60 Speed
Nature: Adamant
- Agility
- Ice Punch
- Meteor Punch
- Zen Headbutt/ Thunder Punch
Metagross is a really good bulky Pokemon. It can also run an Agility set, so it can set up Agility while tanking some hits, and then proceed to sweep.
Metagross is essentially the epitome of an offensive tank. Great typing, good movepool and really nice stats.
B2W2 specific Pokemon
Since you tagged it B2W2, I'll list some here that are good offensive Pokemon.
Volcarona @ Lum Berry
Ability: Flame Body
EVs: 252 Sp. Atk, 252 Speed, 4 HP
Nature: Timid
- Quiver Dance
- Giga Drain
- Bug Buzz
- Fiery Dance
Volcarona has decent sp. def but poor defence. It has a unique typing and a good movepool though, so that makes up for it. Watch out for Stealth Rock.
Hydreigon @ Expert Belt/ Choice Specs/ Choice Scarf
Ability: Levitate
EVs: 252 Sp. Atk, 252 Speed, 4 HP
Nature: Modest/ Timid
- Draco Meteor
- Dark Pulse
- Flamethrower
- Roost/ Surf
Hydreigon has passable defences, as most Dragons do.
Excadrill @ Air Balloon
Ability: Sand Rush/ Mold Breaker (Sand Rush for any Sandstorm team)
EVs: 252 Atk, 252 Speed, 4 HP
Nature: Jolly
- Swords Dance
- Earthquake
- Rock Slide
- Iron Head
While Excadrill has low defences, it's part steel so that resistance to most things will be able to let it take a hit and set up swords dance.