Mega Venusaur should be used over regular Venusaur in all cases. The extra bulk and Thick Fat ability help it big-time:
-Giga Drain
-Sludge Bomb
-Leech Seed/Sleep Powder/Earthquake/Knock Off
-Synthesis
Nature: Bold/Relaxed
EVs: 252 HP/240 Def/16 Spe
Item: Venusaurite
or
-Giga Drain
-Sludge Bomb
-Hidden Power (Fire)
-Synthesis
Nature: Modest
EVs: 232 HP/252 SAtk/4 SDef/20 Spe
Item: Venusaurite
Talonflame can get away with an Adamant nature, since Gale Wings gives priority to Brave Bird:
-Swords Dance
-Flare Blitz
-Brave Bird
-Roost
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb/Sharp Beak/Sky Plate
Ability: Gale Wings
or
-Flare Blitz
-Brave Bird
-U-turn
-Tailwind/Roost
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Band/Sharp Beak/Sky Plate
Ability: Gale Wings
or
-Bulk Up
-Brave Bird
-Roost
-Taunt/Will-o-Wisp
Nature: Careful
EVs: 248 HP/8 Def/252 SDef
Item: Leftovers
Ability: Gale Wings
or
-Brave Bird
-Taunt
-Will-o-Wisp
-Roost
Nature: Careful
EVs: 248 HP/252 SDef/8 Spe
Item: Leftovers
Ability: Gale Wings
or
-Swords Dance
-Flare Blitz
-Brave Bird
-Natural Gift
Nature: Jolly
EVs: 120 HP/252 Atk/136 Spe
Item: Liechi Berry/Salac Berry
Ability: Gale Wings
Swampert isn't that useful anymore, since the power creep made it difficult for it to wall anything effectively. Better Water Pokemon to use in its place down here:
Gastrodon:
-Scald
-Earth Power/Ice Beam/Earthquake
-Toxic
-Recover
Nature: Bold/Relaxed
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Ability: Storm Drain
Quagsire:
-Scald
-Earthquake
-Toxic
-Recover
Nature: Relaxed
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Ability: Unaware
Wash Rotom:
-Volt Switch
-Hydro Pump
-Will-o-Wisp
-Pain Split/Rest
Nature: Bold/Calm
EVs: 248 HP/216 Def/44 Spe (Bold) or 248 HP/216 SDef/44 Spe (Calm)
Item: Leftovers/Chesto Berry
Greninja:
-Hydro Pump
-Ice Beam
-Grass Knot/Hidden Power (Grass)/Extrasensory/Spikes
-Dark Pulse/Hidden Power (Fire)/Extrasensory/Spikes
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb
Ability: Protean
Slowbro:
-Scald
-Psyshock/Ice Beam/Fire Blast
-Toxic/Thunder Wave
-Slack Off
Nature: Bold
EVs: 252 HP/232 Def/24 SDef
Item: Leftovers/Rocky Helmet
Ability: Regenerator
Azumarill:
-Waterfall
-Aqua Jet
-Play Rough
-Superpower/Knock Off
Nature: Adamant
EVs: 228 HP/252 Atk/28 Spe (former 3 items) or 16 HP/252 Atk/240 SDef (latter item)
Item: Choice Band/Mystic Water/Splash Plate/Assault Vest
Ability: Huge Power
or
-Belly Drum
-Aqua Jet
-Play Rough
-Waterfall/Superpower
Nature: Adamant
EVs: 92 HP/252 Atk/164 Spe
Item: Sitrus Berry
Ability: Huge Power
One of your slots should have a Stealth Rock user. Examples down here:
Tyranitar:
-Stealth Rock
-Crunch
-Stone Edge/Ice Beam
-Earthquake/Fire Blast
Nature: Relaxed
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers
Ability: Sand Stream
Therian Landorus:
-Stealth Rock
-Earthquake
-U-turn
-Stone Edge/Rock Slide/Knock Off
Nature: Impish
EVs: 152 HP/252 Def/104 Spe
Item: Leftovers
Garchomp:
-Stealth Rock
-Outrage/Dragon Claw
-Earthquake
-Fire Blast/Swords Dance
Nature: Naive/Jolly
EVs: 252 Atk/4 SAtk/252 Spe
Item: Lum Berry/Focus Sash/Rocky Helmet
Since Talonflame is 4x weak to Rock, especially coming from Stealth Rock, Rapid Spin/Defog support is necessary to get rid of said entry hazard, among others:
Starmie:
-Hydro Pump
-Psyshock/Thunderbolt
-Ice Beam
-Rapid Spin
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb/Leftovers
Ability: Natural Cure/Analytic
or
-Scald
-Reflect Type
-Rapid Spin
-Recover
Nature: Timid
EVs: 248 HP/20 Def/16 SDef/224 Spe
Item: Leftovers
Ability: Natural Cure
Tentacruel:
-Scald
-Acid Spray
-Sludge Bomb/Knock Off
-Rapid Spin
Nature: Bold
EVs: 252 HP/224 Def/32 Spe
Item: Black Sludge
Ability: Liquid Ooze
Mandibuzz:
-Foul Play
-Roost
-Defog
-Taunt/Whirlwind
Nature: Bold
EVs: 248 HP/136 Def/108 SDef/16 Spe
Item: Leftovers
Ability: Overcoat
Skarmory:
-Roost
-Defog
-Brave Bird/Counter
-Taunt/Whirlwind
Nature: Impish
EVs: 252 HP/252 Def/4 SDef
Item: Shed Shell
Ability: Sturdy
Excadrill:
-Earthquake
-Iron Head
-Rock Slide
-Rapid Spin
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Choice Scarf/Air Balloon/Life Orb
Ability: Mold Breaker/Sand Rush (latter only if you're using Tyranitar)
