Venusaur

Venusaur is a Grass-Poison type Pokemon introduced in Generation I, in the games Red and Green. It evolves from Ivysaur at Level 32. It can Mega Evolve into Mega Venusaur when it holds the Venusaurite. It has the ability to Gigantamax.

Competitive Usage
Venusaur (♂) Venusaur (♂) Venusaur (♂)  Venusaur (♂) Venusaur (♂) Venusaur (♂) Venusaur (♀) Venusaur (♂) Venusaur (♂) Venusaur (♂) Venusaur (♂) Venusaur (Any) Venusaur (Any) Venusaur (♀) Venusaur (♂) Venusaur (♂) Venusaur (♂) Venusaur (Any) Venusaur (Any) Venusaur (Any) Venusaur (Any) Venusaur (Any) Venusaur (Any) Venusaur (♂) Venusaur (♂) Venusaur (♂) Venusaur (Any) Venusaur (Any) Venusaur (Any) Venusaur (Any) Venusaur (Any)
 * Item: Black Sludge
 * Ability: Chlorophyll
 * EVs: 28 Defense, 252 Special Attack, 228 Speed
 * Modest Nature (+Special Attack, -Attack)
 * Growth
 * Solar Beam
 * Hidden Power (Fire)
 * Sludge Bomb
 * Item: Life Orb
 * Ability: Chlorophyll
 * EVs: 176 Attack, 128 Special Attack, 204 Speed
 * Naughty Nature (+Attack, -Special Defense)
 * Solar Beam
 * Earthquake
 * Hidden Power (Fire)
 * Growth
 * Item: Leftovers
 * Ability: Overgrow
 * EVs: 64 HP, 96 Attack, 96 Defense, 252 Special Defense
 * Careful Nature (+Special Defense, -Special Attack)
 * Curse
 * Seed Bomb
 * Synthesis
 * Earthquake
 * Item: Leftovers
 * Ability: Overgrow
 * EVs: 96 HP, 252 Attack, 32 Defense, 128 Special Defense
 * Adamant Nature (+Attack, -Special Attack)
 * Curse
 * Earthquake
 * Sludge Bomb
 * Leech Seed
 * Item: Life Orb
 * Ability: Chlorophyll
 * EVs: 252 Attack, 252 Speed, 4 HP
 * Jolly Nature (+Speed, -Special Attack)
 * Sleep Powder/Petal Blizzard
 * Growth/Swords Dance
 * Outrage
 * Earthquake
 * Item: Leftovers
 * Ability: Chlorophyll
 * EVs: 4 HP, 252 Special Attack, 108 Special Defense, 144 Speed
 * Modest Nature (+Special Attack, -Attack)
 * Hidden Power (Fire)
 * Sleep Powder
 * Sludge Bomb
 * Solar Beam
 * Item: Black Sludge
 * Ability: Overgrow/Chlorophyll
 * EVs: 252 Attack, 196 Defense, 60 Special Defense/40 HP, 252 Attack, 216 Speed
 * Adamant Nature (+Attack, -Special Attack)
 * Curse/Swords Dance/Growth
 * Razor Leaf/Power Whip
 * Earthquake
 * Frustration
 * Item: Life Orb
 * Ability: Chlorophyll
 * EVs: 4 HP, 252 Special Attack, 252 Speed
 * Timid Nature (+Speed, -Attack)
 * Growth
 * Giga Drain
 * Sludge Bomb
 * Hidden Power (Fire)
 * Item: Venusaurite
 * Ability: Chlorophyll --> Thick Fat
 * EVs: 252 HP, 252 Special Attack, 4 Defense
 * Modest Nature (+Special Attack, -Attack)
 * Giga Drain
 * Sludge Bomb
 * Hidden Power (Fire)/Sleep Powder
 * Synthesis
 * Item: Black Sludge
 * Ability: Overgrow
 * EVs: 252 HP, 4 Attack, 252 Special Defense
 * Gentle Nature (+Special Defense, -Defense)
 * Giga Drain
 * Leech Seed
 * Bind
 * Protect
 * Item: Miracle Seed
 * Ability: Overgrow
 * EVs: 60 HP, 196 Attack, 252 Speed
 * Jolly Nature (+Speed, -Special Attack)
 * Swords Dance
 * Earthquake
 * Razor Leaf
 * Power Whip
 * Item: Leftovers
 * Ability: Overgrow/Chlorophyll
 * EVs: 252 Special Attack, 252 HP
 * Modest Nature (+Special Attack, -Attack)
 * Leech Seed
 * Sunny Day
 * Solar Beam
 * Synthesis
 * Item: Big Root
 * Ability: Overgrow
 * EVs: 240 Defense, 140 Special Attack, 130 Special Defense
 * Bold Nature (+Defense, -Attack)
 * Leech Seed
 * Substitute
 * Protect
 * Sludge Bomb
 * Item: Venusaurite
 * Ability: Overgrow
 * EVs: 252 HP, 4 Defense, 252 Special Defense
 * Sassy Nature (+Special Defense, -Speed)
 * Leech Seed
 * Giga Drain
 * Sludge Bomb
 * Earthquake
 * Item: Black Sludge
 * Ability: Chlorophyll
 * EVs: 252 Attack, 252 Speed, 6 HP
 * Jolly Nature (+Speed, -Special Attack)
 * Swords Dance
 * Petal Blizzard
 * Earthquake
 * Synthesis
 * Item: Leftovers
 * Ability: Chlorophyll
 * EVs: 252 Special Attack, 252 Special Defense, 4 Defense
 * Modest Nature (+Special Attack, -Attack)
 * Toxic
 * Venoshock
 * Solar Beam
 * Leech Seed/Synthesis
 * Item: Venusaurite
 * Ability: Overgrow/Chlorophyll --> Thick Fat
 * EVs: 252 Defense, 4 Special Attack, 252 Special Defense
 * Bold Nature (+Defense, -Attack)
 * Toxic
 * Amnesia/Protect
 * Leech Seed/Synthesis
 * Petal Dance/Venoshock
 * Item: Venusaurite
 * Ability: Overgrow
 * EVs: 252 HP, 252 Special Defense, 4 Defense
 * Bold Nature (+Defense, -Attack)
 * Giga Drain
 * Leech Seed
 * Ingrain
 * Sleep Powder
 * Item: Black Sludge/Venusaurite
 * Ability: Chlorophyll/Thick Fat
 * EVs: 252 Defense, 252 Special Defense, 4 HP
 * Bold Nature (+Defense, -Attack)/Calm Nature (+Special Defense, -Attack)
 * Sleep Powder
 * Sludge Bomb/Solar Beam
 * Synthesis
 * Growth
 * Item: Black Sludge
 * Ability: Overgrow
 * EVs: 252 Special Attack
 * Modest Nature (+Special Attack, -Attack)
 * Leech Seed
 * Protect
 * Growth
 * Energy Ball./Giga Drain
 * Item: None
 * Ability: Chlorophyll
 * EVs: 252 HP, 148 Defense, 80 Special Attack, 28 Special Defense
 * Bashful Nature
 * Growth
 * Sweet Scent
 * Solar Beam
 * Razor Leaf
 * Item: Venusaurite
 * Ability: Thick Fat
 * EVs: 180 HP, 48 Attack, 88 Defense, 72 Special Attack, 120 Special Defense
 * Brave Nature (+Attack, -Speed)
 * Synthesis/Growth
 * Power Whip/Solar Beam
 * Toxic/Leech Seed
 * Venoshock/Grass Pledge
 * Venusaurite
 * Ability: Thick Fat
 * EVs: 252 Defense, 252 HP, 4 Attack
 * Impish Nature (+Defense, -Special Attack)
 * Knock Off
 * Earthquake
 * Swords Dance
 * Synthesis
 * Item: Heat Rock
 * Ability: Chlorophyll
 * EVs: 252 HP, 203 Special Defense, 55 Defense
 * Bold Nature (+Defense, -Speed)
 * Sunny Day
 * Growth
 * Synthesis
 * Solar Beam
 * Item: Venusaurite
 * Ability: Overgrow
 * EVs: 8 HP, 250 Attack, 250 Special Attack
 * Lonely Nature (+Attack, -Defense)
 * Sludge Bomb
 * Earthquake
 * Petal Dance
 * Outrage
 * Item: Rocky Helmet/Leftovers/Sitrus Berry/Black Sludge/Dread Plate
 * Ability: Overgrow
 * EVs: 4 HP, 252 Defense, 252 Special Defense
 * Relaxed Nature (+Defense, -Speed)/Sassy Nature (+Sp.Def, -Speed)/Quiet (+Sp.Atk, -Spd)/Brave (+Atk, -Spd)
 * Sludge Bomb
 * Giga Drain
 * Knock Off
 * Curse
 * Item: Firium Z
 * Ability: Chlorophyll
 * EVs: 252 Special Attack, 252 Speed
 * Modest Nature (+Special Attack, -Attack)
 * Sunny Day
 * Solar Beam
 * Sludge Bomb/Hidden Power (Fire)/Toxic
 * Synthesis
 * Item: Venusaurite
 * Ability: Overgrow
 * EVs: 252 HP, 252 Special Attack, 4 Special Defense
 * Modest Nature (+Special Attack, -Attack)
 * Sludge Bomb
 * Giga Drain
 * Synthesis
 * Hidden Power (Fire)
 * Item: Black Sludge/Lum Berry
 * Ability: Overgrow
 * EVs: 252 HP, 4 Defense, 252 Special Defense
 * Bold Nature (+Defense, -Attack)/Calm Nature (+Special Defense, -Attack)
 * Synthesis/Ingrain
 * Sludge Bomb/Toxic
 * Giga Drain
 * Petal Dance/Energy Ball
 * Item: Black Sludge
 * Ability: Chlorophyll
 * EVs: 252 HP, 4 Defense, 252 Special Defense
 * Bold Nature (+Defense, -Attack)/Modest Nature (+Special Attack, -Attack)
 * Leech Seed
 * Synthesis/Giga Drain
 * Growth/Protect
 * Solar Beam
 * Item: Black Sludge/Power Herb
 * Ability: Chlorophyll
 * EVs: 252 HP, 4 Defense, 252 Special Defense
 * Adamant (+Atk,-Sp.Atk)/Impish (+Def,Sp.Atk)/Rash (+Sp.Atk,-Sp.Def)/Jolly (+Spe,-Sp.Atk)
 * Earthquake
 * Petal Blizzard/Growth
 * Leaf Storm/Power Whip
 * Skull Bash/Swords Dance

If you'd like to add your set, feel free to!