1. Bulky Tank
Venusaur @ Black Sludge / Lum Berry
Ability: Overgrow
EVs: 252 HP / 4 Def / 252 SpD
Nature: Bold / Calm
-Synthesis / Ingrain (Ingrain if there are no Fire or Flying types. This thing can probably handle Psychic and Ice types.)
-Sludge Bomb / Toxic
-Giga Drain
-Petal Dance / Energy Ball
Black Sludge if you're thirsting for more health, Lum Berry if you want a STAB Petal Dance, at the cost of confusion. I prefer Ingrain, but Synthesis is an instaheal for emergencies. Sludge Bomb for the heck of it, STAB, and quite a good chance of poisoning. Toxic to badly poison them, Sludge Wave is a possibility but I much prefer Sludge Bomb over all of them. Giga Drain for health recovery (especially on Pokemon like Whiscash, Swampert, Gastrodon, etc.) and Energy Ball for STAB.
2. Special Sunny Sweeper
Ahh... my favorite.
Venusaur @ Black Sludge
Ability: Chlorophyll
EVs: 252 HP / 4 Def / 252 SpD
Nature: Bold / Modest
-Leech Seed
-Synthesis/Giga Drain
-Growth/Protect
-Solar Beam
Leech Seed to drain the opponent's health, then Giga Drain a couple of times, cuz wynaut? Growth is to boost the Special Atk and Protect is there solely so you won't be a Taunt victim, you know? Now pull off a Growth Sun-Powered STAB Solar Beam for a mind-boggling 240 damage
3. Physical Sweeper
Venusaur @ Black Sludge / Power Herb
Ability: Chlorophyll
EVs: 252 HP / 4 Def / 252 Sp Def
Nature: Adamant / Impish / Rash / Jolly
-Earthquake
-Petal Blizzard/Growth
-Leaf Storm/Power Whip
-Skull Bash/Swords Dance
This is surprising. Expect me to run a special set? Think again. Start with a subtle hint: Leaf Storm. Since it's the only special move in this set, you should be O.K. Earthquake to get rid of Fire types (watch out for Charizard!).
Petal Blizzard/Growth next. Growth shouldn't give you away...yet. Petal Blizzard for STAB. After raging at all the Fire types start spamming Petal Blizzard/Earthquake.