Magnezone
Type: Electric / Steel
Base Stats: 70 HP / 70 Atk / 115 Def / 130 SpA / 90 SpD / 60 Spe
Ability: Magnet Pull / Sturdy / Analytic
Magnezone brings to the competitive scene a mammoth base 130 Special Attack, enough to seriously dent everything but the bulkiest walls or resists. Although its good STABs coupled with its sheer attacking prowess can make it a hard Pokemon to switch into, for some opponents, it's much harder to switch out
. Thanks to Magnezone's amazing ability Magnet Pull, all Steel-types (apart from Aegislash) are trapped and cannot switch, allowing Magnezone to reliably dispatch most of them with one of its moves and open up a sweep for a teammate. To take it one step further, Magnezone can even use the Steel-types that cannot hurt it, such as Ferrothorn, as setup bait and boost up to extremely powerful levels. Considering Magnezone's ability to take one of the most useful types in the game and turn it into a huge liability for the opponent, Magnezone must be evaluated as a severely game-changing opponent.
Rotom-W
Type: Electric / Water
Base Stats: 50 HP / 65 Atk / 107 Def / 105 SpA / 107 SpD / 86 Spe
Ability: Levitate
Although it is typically seen sporting a defensive set, it cannot be denied that one of Rotom-W's selling points is the awesome coverage it gets from its STABs alone. With a respectable base 105 Special Attack, Rotom-W can do significant damage to a number of opponents with the appropriate move. Thanks to its access to STAB Volt Switch, Rotom-W can not only afford to run items such as Choice Scarf, but also grab momentum on a whim, as most Ground-types fear Rotom-W's STAB Hydro Pump too much to switch in. Overall, Rotom-W's offensive qualities and flexibility allow it to be an effective offensive presence that cannot be underestimated.
Reserving
Goodra (defensive). Also,
Jukain, TRC already covered offensive Starmie
here, so it shouldn't be up for grabs. Same deal with defensive Roserade, which Zam's Moustache completed
here.