But what if:
Mega Carnivine:
Grass/Dark
HP: 74
Atk: 135 (+35)
Def: 107 (+35)
SpA: 105 (+15)
SpD: 107 (+35)
Spe: 26 (-20)
Ability: Strong Jaw
New Moves: Psychic Fangs, Earth Power, Extrasensory, Wide Guard, Sucker Punch
Omnomnom.
It's still rather crappy outside of Trick Room, and probably won't ever see even the light of UU, but hey, something's better than nothing. STAB Strong Jaw Crunch can put a dent in most things, and access to Psychic Fangs and Earth Power adds decent coverage. Sucker Punch can help mitigate its terrible speed somewhat; at any rate, if Victreebel gets it, no reason why its fellow carnivorous plant shouldn't.
Ironic that an insectivore is x4 weak to Bug attacks, especially U-Turn. That'll come to bite it in the back, har har.