Victreebel is one of the best Grass-types due to its great Attack and Special, letting it hit opponents hard from both sides. It can use Swords Dance effectively with Body Slam and Hyper Beam, maxing its Attack after two uses of Swords Dance. Razor Leaf OHKOs Rock / Ground Pokémon that think they can wall Victreebel's Normal attacks, and will cause massive damage to any Water-types. However, it is limited in its effectiveness due to it low Speed and weakness to Psychic. All in all, Victreebel is a great Pokémon to bring in on a paralyzed team, because of its ability to sweep with either of its sets quite easily.
Victreebel has the attack stats to pull off a mixed sweeper role effectively—the problem lies in its mediocre Speed. If you save Victreebel for late-game or when the majority of the opponent's Pokémon are paralyzed, it will cause havoc. A Swords Dance-boosted Body Slam will cause huge damage to anything not named Golem or Rhydon, which Razor Leaf can take care of quite easily. Sleep Powder gives Victreebel a turn to Swords Dance while the opponent switches or stays in and does nothing.
The Body Slam versus Hyper Beam decision is entirely up to preference, but Body Slam has a slight edge. Hyper Beam is more powerful, but if it doesn't OHKO the opponent's Pokémon, Victreebel will be hurt during its recharging turn. Body Slam is a much more consistent attack, due to the lack of a recharging turn and the bonus of paralysis. Predicting a switch and inflicting paralysis with Body Slam keeps Victreebel alive and healthy to continue sweeping.
As said before, Victreebel is an amazing late-game Pokémon. Bring this in on any paralyzed Pokémon and proceed to use Wrap to whittle down your opponent's health until it's in range for a surefire OHKO from Razor Leaf or Hyper Beam, rinse, and repeat. Stun Spore is in this set to paralyze anything faster than Victreebel so that it can use Wrap more effectively. This set relies heavily on the opponent's being slower or paralyzed, since, if it isn't, Victreebel will be at a severe disadvantage and very ineffective for the most part.
There's really nothing else for Victreebel to do besides the sets listed above. Growth can raise Victreebel's Special, but the boost doesn't matter when using Razor Leaf since critical hits don't take into account the boost. Reflect can raise his Defense a bit which can be useful on the Wrapper set. Mimic can maybe get you Earthquake to smack Gengar, but that's highly unlikely.
Checks and Counters
Gengar completely walls Victreebel, since it resists Razor Leaf and is immune to Body Slam and Hyper Beam; it does not like being paralyzed by Victreebel's Stun Spore, though. Zapdos, Moltres, and Articuno take very little damage from Razor Leaf and can hit back with a STAB super effective attack (Drill Peck, Fire Blast, Ice Beam, respectively), although, just like for Venusaur, the three birds must beware of paralysis, especially Zapdos and Moltres. Psychic-types (except Starmie and Slowbro) can come in on a Razor Leaf and can do substantial damage to Victreebel with a STAB super effective Psychic.