Serperior:
Black: "It can stop its opponents' movements with just a glare. It takes in solar energy and boosts it internally."
If Serperior uses Glare, the opponent can not move at all (unless Serperior is KO'd or switched out), not even to switch out. Serperior's speed doubles in the sun.
White: "They raise their heads to intimidate opponents but only give it their all when fighting a powerful opponent."
Serperior gets the ability Intimidate. If the opponent is a lower level than Serperior, its attacks do half damage.
B2/W2: "It only gives its all against strong opponents who are not fazed by the glare from Serperior's noble eyes."
Serperior's attacks do 50% more damage against a higher-level opponent. However, an opponent of higher level is immune to Serperior's glare.
This might be the only metagame in pokemon in the 90s in level are used.
Snivy:
Black: "It is very intelligent and calm. Being exposed to lots of sunlight makes its movements swifter."
Snivy is immune to the effects of Torment, Taunt, and Attract. Its speed doubles in sun.
White: "They photosynthesize by bathing their tails in sunlight. When they are not feeling well, their tails droop."
If Snivy is affected by a status condition, its tail droops.
BW2: "Being exposed to sunlight makes its movements swifter. It uses vines more adeptly than its hands."
When Snivy uses Vine Whip, it hits for triple normal damage.
Servine:
Black: "It moves along the ground as if sliding. Its swift movements befuddle its foes, and it then attacks with a vine whip."
An oppenent is automatically confused when Servine switches in.
White: "They avoid attacks by sinking into the shadows of thick foliage. They retaliate with masterful whipping techniques."
Servine always has +2 evasion. It can learn Power Whip, which it must use to retaliate against a foe that misses.
BW2: "When it gets dirty, its leaves can't be used in photosynthesis, so it always keeps itself clean."
If Servine is hit by Mud Bomb, Mud Slap, Sand-Attack, Sludge Bomb, Sludge Wave, etc., Servine loses a turn.
Victini:
White: "It creates an unlimited supply of energy inside its body, which it shares with those who touch it."
BW2: "When it shares the infinite energy it creates, that being's entire body will be overflowing with power."
If a pokemon hits it with a contact move, its HP is fully restored. Victini can never faint and fully restores its HP immediately after taking damage.
On a side note, that would be how trainers with Victini always win.
I say we should vote between OHKO clause or Victini, as it would be too powerful without OHKO moves to bypass it.