Looking at the 'Big 12' leads, I have found that one pokemon is capable of countering ALL of them.
Rotom-C @ Choice Specs
252 Sp.Attack, 252 Speed, 4 HP
Modest
Leaf Storm
Shadow Ball
Thunderbolt
Trick
I calculated damage on all of the standard lead sets for the 'big 12' barring Ninjask, who is OHKO'ed by most things, and has Sash anyway, and the results were pleasing. Please note that these are in useage order.
Metagross: Thunderbolt = 66.76% - 78.57% (Outsped)
Azelf: Thunderbolt = 192.72% - 226.44% (Sashed, but can't 2HKO)
Swampert: Leaf Storm = 237.16% - 279.05% (Outsped)
Jirachi: Thunderbolt = 58.53% - 68.77%
Aerodactyl: Thunderbolt = 186.75% - 219.54% (Sashed, but can't 2HKO)
Infernape: Thunderbolt = 100.34% - 118.09%
Hippowodon: Leaf Storm = 110.24% - 129.76% (Outsped)
Ninjask: Thunderbolt = 2HKO due to Sash
Bronzong: Thunderbolt = 53.85% - 63.31% (Outsped)
Tyranitar: Leaf Storm = 91.27% - 107.23% (Outsped)
Heatran: Thunderbolt = 65.43% - 77.16% (Outsped without + Speed)
Abomasnow: Shadow Ball = 66.98% - 78.82% (Outsped)
As you can see, only Metagross, Jirachi, Heatran, Abomasnow and Bronzong are not OHKO'ed (Tyranitar CAN live), and of these, only Heatran and Abomasnow can do anything significant back, unless Jirachi flinchaxes it's way past. Rotom is immune to Explosion, that so many Suicide leads carry, and also Fighting types, and EQ. Rotom is bulky enough to take a hit or two with it's inferior speed, barring possibly Tyranitar, and KO the lead back, especially as most will either set up rocks, or switch. In the event of a switch, anything that is not a Ground type will take a heavy blow from Thunderbolt, those who are not Normals will be hurt by Shadow Ball, and Leaf Storm brings the pain on almost anything else not with a X4 resist.
Bronzong, although a possible 3HKO due to lefties, can hardly scratch Rotom, due to it's low speed, and resistance to Gyro Ball, and Immunity to Explosion and Earthquake. Same with Metagross's Meteor Mashes.
Basically, Rotom can stop about half of the common leads from setting up Rocks, and score a OHKO on half of them as well.
You COULD add HP Fire over Trick, for a OHKO on Abomasnow, and to deal increased damage to the Steels, but Trick aids in later game, where Rotom has been recalled, and sent out against a wall.
I see Rotom-C becoming a new Anti-Lead...