Anything Delphox can do, Charizard, Infernape, Talonflame and Darmanitan can do better. Delphox's move pool is pretty shallow; outside of Hidden Power, it can't do much to Hydreigon and Houndoom:
Charizard:
-Dragon Dance
-Flare Blitz/Fire Punch
-Dragon Claw/Outrage
-Earthquake/Roost
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Charizardite X
Ability: Blaze
or
-Dragon Dance
-Dragon Claw
-Fire Punch/Earthquake
-Roost
Nature: Adamant
EVs: 144 HP/244 Atk/120 Spe
Item: Charizardite X
Ability: Blaze
or
-Fire Punch/Earthquake
-Dragon Claw
-Will-o-Wisp
-Roost
Nature: Careful
EVs: 248 HP/148 SDef/112 Spe
Item: Charizardite X
Ability: Blaze
or
-Fire Blast
-Solar Beam
-Focus Blast
-Dragon Pulse/Roost
Nature: Timid/Modest
EVs: 4 Def/252 SAtk/252 Spe
Item: Charizardite Y
Infernape:
-Fire Blast/Flare Blitz
-Close Combat
-Thunder Punch
-Grass Knot/Mach Punch/Hidden Power (Ice)
Nature: Hasty/Naive
EVs: 168 Atk/88 SAtk/252 Spe
Item: Life Orb/Expert Belt
Talonflame:
-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
-Taunt/Will-o-Wisp
-Roost
Nature: Careful
EVs: 248 HP/8 Def/252 SDef
Item: Leftovers
Ability: Gale Wings
Darmanitan:
-Flare Blitz
-U-turn
-Earthquake/Superpower
-Rock Slide/Superpower
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb/Choice Band/Choice Scarf
Ability: Sheer Force
Lucario is lacking in power here. Considering that you may be using another Mega in Charizard, it's better off not using its Mega Stone; it's viable without it:
-Swords Dance
-Close Combat
-Extreme Speed
-Crunch/Ice Punch/Earthquake/Shadow Claw
Nature: Adamant/Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb/Lucarionite
or
-Nasty Plot
-Aura Sphere
-Flash Cannon
-Shadow Ball/Dark Pulse/Vacuum Wave
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Lucarionite
Ability: Inner Focus/Steadfast
Venusaur is only good in its Mega form outside of Sun teams, though Chlorophyll Venusaur is usable with Charizard Y:
-Giga Drain
-Sludge Bomb
-Sleep Powder/Leech Seed/Hidden Power (Fire)/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/Sleep Powder
Nature: Modest
EVs: 252 HP/252 SAtk/4 SDef
Item: Venusuarite
or (Charizard Y is mandatory here)
-Giga Drain/Leaf Storm
-Sludge Bomb
-Hidden Power (Fire)/Earthquake
-Synthesis/Sleep Powder
Nature; Modest/Rash
EVs: 28 Atk/252 SAtk/228 Spe
Item: Life Orb
Ability: Chlorophyll
As people may frown down on you using Xerneas (an Uber), another Fairy alternative is Azumarill. After Pokemon Village, you won't be needing Cut anymore. Since you also have a Water Pokemon in Greninja, you'll have to pick one of the two. I'll explain how the last slot should be used later:
Azumarill:
-Waterfall
-Aqua Jet
-Play Rough
-Superpower/Knock Off
Nature: Adamant
EVs: 228 HP/252 Atk/28 Spe
Item: Choice Band/Mystic Water/Splash Plate
Ability: Huge Power
or
-Belly Drum
-Aqua Jet
-Play Rough
-Waterfall/Superpower
Nature: Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Sitrus Berry
Ability: Huge Power
or
-Waterfall
-Aqua Jet
-Play Rough
-Knock Off
Nature: Adamant
EVs: 16 HP/252 Atk/240 SDef
Item: Assault Vest
Ability: Huge Power
Greninja:
-Hydro Pump/Surf
-Ice Beam
-Extrasensory
-Dark Pulse/Hidden Power (Fire/Grass)/Grass Knot/Spikes
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Life Orb/Focus Sash
Ability: Protean
However, Greninja is just too frail to make use of Rocky Helmet. Pokemon such as Ferrothorn and Garchomp have enough bulk to make use of the item.
The last slot should be devoted to a hazard setter and hazard clearer; Skarmory can fulfill both roles:
-Whirlwind
-Roost
-Stealth Rock/Spikes/Brave Bird
-Defog/Brave Bird
Nature: Bold/Impish
EVs: 252 HP/252 Def/4 SDef or 252 HP/16 Def/240 SDef
Item: Leftovers/Rocky Helmet
Ability: Sturdy
Since Defog is exclusive to Skarmory in Gen IV, consider Mandibuzz as well:
-Foul Play
-Defog
-Roost
-Knock Off/Whirlwind/Toxic
Nature: Impish/Bold
EVs: 248 HP/252 Def/8 SDef
Item: Leftovers/Rocky Helmet
Ability: Overcoat
Wow.. umm.. first let me thank you XD
I was going to replace Delphox anyway, it was just my starter, thank you for the suggestions. I'll replace it with Mega Charizard X. (or Y?)
As for Lucario, I might replace it with a new Lucario that I'll breed and train... or is there a better option?
As I will only be playing mainly with my friends, using Xerneas won't be a problem I think (Also cus I really like Xerneas....) But if it stays in my team I will definitely change its move set. Again thank you ^^
I only equipped Greninja with Rocky Helmet simply because otherwise it probably wouldn't be holding an item because I have no idea. It's too frail huh.... I agree XD
As for bulk, I was thinking of using Blissey (I know it's overused and all...) but again, I wouldn't be playing against competitive players. And for some reason I thought Gengar would also be quite nice... Any suggestions on those would be very much appreciated ^^
And pretty much every team should have a hazard move huh... you're right I should add them...