Wow, a pretty good team, I have to say, but lets have a look. Now Im not the best team-rater, in not too competitive, but I'll give it a shot ;)
Venusaur
Your Venusaur is looking pretty solid. I'd suggest making its nature Relaxed (+Def, -Spd) instead though, just to give earthquake some more power, anyway, most of what Mega Venusaur will be going up against (Psychic, Flying) are gonna be much faster than it, and since its not even invested in speed, I suggest relaxed. Otherwise than that you've got a good moveset, Ive never seen a leech seed giga drain moveset before, but I guess it could work out.
Breloom
Okay, this Breloom is looking pretty sketchy, its DEVASTATINGLY weak to flying, who you do not have really covered at all, apart from Garchomp who you rely on for too many things anyway (I'll be getting on to that anyway). Personally I'd 'dump' Breloom. He's a good pokemon but he doesn't really work well on your team, especially since you already have a grass type. I suggest:
Conkeldurr @ Flame Orb
EVs: 252 Atk 252 HP 4 Def
Ability: Guts
Nature: Adamant
-Superpower
-Mach Punch
-Earthquake
-Payback
Or
Conkeldurr @ Leftovers
EVs: 252 Atk 252 HP 4 Def
Abilty: Iron Fist
Nature: Adamand
-Drain Punch
-Mach Punch
-Bulk Up
-Payback
Scizor
Perfect. A very good scizor, works with your team. Cant punch a hole in it.
Azumarill
Okay, a bit of a weird moveset. I get why you need to aqua jet for priority, but any pokemon that you need priority for you shouldn't have Azumarill. Replace Aqua Jet with Aqua Tail/Waterfall (WF for the 20% flinch and accuracy, AT for the power), you need the power, and with Huge Power, you cant waste that. Honestly I dont know why you're running Protect on it, none of your pokemon can inflict status conditions anyway. Replace it with Ice Punch immeediiaattlyyy
Garchomp
Alright, you can not put Choice Band on it. You rely on it to take care of way to many pokemon. Replace it with leftovers or something of that sort, otherwise its pretty good ;)
Talonflame
Replace shell bell with leftovers, if you cant because you've already put it on one of the other pokemon I suggested, keep the shell bell, the only reason I suggest leftovers is because although the shell bell gives more HP on OHKO moves, you wont regain health on non-killing moves which leftovers do. (Basically leftovers are reliable) but the shell bell will do fine. Otherwise good coverage, good moveset.
Summery
A pretty good team, but please take the things I said into consideration. Also, you are too weak to flying, and psychic. You need to buff up your azumarill a little, and not have to rely on your Garchomp so much, but still a very good team.
