Alright, so let's do a little analysis here...
We're going to assume that you have full 31 IVs in every stat:
Ninetales @ Leftovers
Ability: Flash Fire
Shiny: Yes
EVs: 4 HP / 124 SpA / 124 SpD / 252 Spe (You're missing 4 EVs)
Modest Nature
- Hypnosis
- Energy Ball
- Flamethrower
- Extrasensory
Crobat @ Toxic Plate
Ability: Infiltrator
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
- X-Scissor
- Steel Wing
- Cross Poison
- Aerial Ace
Lucario @ Lucarionite
Ability: Inner Focus
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
- Poison Jab
- Iron Tail
- Ice Punch
- Drain Punch
Sylveon @ Pixie Plate
Ability: Pixilate
Shiny: Yes
EVs: 4 HP / 252 SpA / 252 SpD
Modest Nature
- Iron Tail
- Dazzling Gleam
- Shadow Ball
- Psyshock
Cacturne @ Sitrus Berry
Ability: Water Absorb
Shiny: Yes
EVs: 252 HP / 252 SpA / 4 Spe
Modest Nature
- Dark Pulse
- Belch
- Energy Ball
- Giga Drain
Seaking @ Leftovers
Ability: Lightning Rod
Shiny: Yes
EVs: 252 HP / 252 Atk / 4 Spe
Adamant Nature
- Waterfall
- Drill Run
- Poison Jab
- Megahorn
After checking every single stat, and every single moveset compatability, this is legal. This is assuming you managed to get 31 IVs in every single stat.
So the second question would be the game you currently have. I know it says ORAS, but are you playing with on X or Y? In that case, this could be the fault of your opponent, as the Mega Pokemon that were introduced in ORAS are not allowed to be in battle with X&Y games.
The next question would be if you used anything to edit these Pokemon. I know you claimed that you breeded everything, but did you use anything, like a Powersave, to edit these Pokemon? If so, the Generation 6 games have ways to detect legitimate Pokemon and those that have been modified in any way.