Carnivine is going to be in the UU section but that doesn't mean its too bad. It has a fairly good moveset that allows it to play as a special and physical sweeper. It doesn't have incredibly good stats, just average but they aren't bad. Overall a pretty decent pokemon but nothing better than that.
Item: Leftovers/ Life Orb
Growth/ Stun Spore/ Sleep Power/ Wring Out
Carnivine's special movepool is very limited but it can still act as a decent special sweeper. It at least has 2 good special moves for sweeping, Energy Ball and Sludge Bomb. Leech Seed in my opinion is one of the best moves in the game as it steady saps away your opponent's health while restoring yours. The last move is fairly important. I recommend Stun Spore simply because Carnivine doesn't have the speed to make good use of Growth and too many pokemon have an ability that works to their advantage when Sleep Powder is used. Wring Out might not be too powerful in certain situations. As for its nature, Carnivine needs the extra attack boost making Modest a handy nature. Any one of its items are fine. Not too bad but with its low speed and barely decent defenses, don't expect too much.
Leech Seed/ Stun Spore
Carnivine also doesn't have a good physical moveset. This one is very risky but use Swords Dance to raise attack power. Leech Seed is recommended to recover lost HP. The last 2 moves are for sweeping and quite decent themselves. This one is much like the previous set with speed being the major problem.
Protect/ Stun Spore/ Synthesis
You might have seen a set similar to this one before with other pokemon. This set is used in the same way, to sap health from opponents while gaining health yourself. Leech Seed will drain health from opponents while healing yourself. Ingrain also to heal and along with leftovers, you'll receive quite a healing. Giga Drain to do damage as well as regain health. With its last move, I suggest Stun Spore just for Carnivine to go first. Be warned tough when you use Ingrain, you can't switch out so be careful. This set isn't great but it is quite rare.
Gender: 50% Female / 50% Male
Species: Bug Catcher Pokemon
Weaknesses: Fire (x2) Ice (x2) Flying (x2) Bug (x2) Poison (x2)
Resistances: Grass (0.5) Water (0.5) Electric (0.5)
Immunities: Ground (Levitate ability)
Diamond: It attracts prey with its sweet-smelling saliva, then chomps it down. It takes a whole day to eat its prey.
Pearl: Hanging from branches with its tentacles, it looks like a plant. It awaits prey, mouth wide open.
Evolution: Doesn't evolve
Rare: Safari Game (Area 2)
Levitate: Avoids damage from ground type attacks. Also avoids normal spikes but is affected like others by Stealth Rock.
National Dex No.: 455
Generation Introduced: 4th
Anime Appearances: Almost every episode when Team Rocket have battled Ash and the group from Two Degrees of Separation.