So I see 3 issues with this team, but isn't that why we are here. At the moment:
1. Fighting are a very potent threat to the team.
2. Your items are a bit of.
3. Some moves are a bit weird.
Scrafty @ Leftovers
Trait: Shed Skin
EVs: 252 HP / 252 Atk / 4 SDef
- Bulk Up
- Drain Punch
I am a big fan of Scrafty, and really like him. At the moment, you are running a very risky set, albeit completely fine. I've just given a alternative option here.
Mamoswine @ Leftovers/Choice Band
Trait: Thick Fat
EVs: 252 HP / 252 Atk / 4 SAtk
- Ice Shard
- Stone Edge
- Stealth Rock/ Superpower
Mamo is definitely one of the most lethal weapons in OU, destroying powerhouses such as Thundrus, Salamance and Dragonite. Bur Special Mamo is weak, even with Rash nature, so here are 2 common variants. Use Lefties with Stealth Rocks or Band with Superpower and obliterate your opponents!
Heracross @ Choice Scarf
EVs: 4 HP / 252 Atk / 252 Spd
- Close Combat
- Stone Edge
Heracross is fine the way he is, but you might want to consider another's variant. Guts is still just fine and I like that you are using it.
Latios @ Life Orb/ Choice Scarf
EVs: 252 SAtk / 4 HP / 252 Spd
- Dragon Pulse
- Hidden Power [Fire]
As of now, Hydreigon weren't realty contributing to the team, so I decided to replace him with something that can kill almost any Figthing type in OU, Latios. The following set I have used with great result myself. Dragon Pulse is mandatory STAB to take down his fellow Dragons. Psychic is often better then Psyshock, but running Psychic make Blissey wall you completely. HP Fire is better than roasted bread on Latios. Very often, your opponent will try to send in a bulky Steel type, such as Ferrothorn or Scizor to deal with the Eon Dragon. 1 HP Fire later, the rage quits should be rolling in. The last slot is kind of a bummer. Surf lets you hit almost anything really hard and whiteout it Heatran will wall you completely whilst not having Recovery severely shortens your lifespan. You can use Choice Scarf if you want to be able to Outspeed Garchomps, Salamances and other Latioses.
Victini @ Choice Band/ Life Orb
Trait: Victory Star
EVs: 252 Atk / 252 Spd / 4 HP
- Bolt Strike
- Zen Headbutt
Charcoal is not a bad item, but it is inferior to Life Orb or Band. Also, mixed Vicitini can work, but I wouldn't use it myself. U-Turn gives momentum and Zen Headbutt is STAB.
Magnezone @ Leftovers/ Air Ballon
EVs: 252 HP / 252 SAtk/ 4 Def
- Thunder/ Thunderbolt
- Hidden Power [Ice]
- Stealth Rock/ Volt Switch
- Thunder Wave
Just as with Charcoal, Magnet is outclassed by most of things. And Hyper Beam should never be used, it is very often not paying of. Thunder is all ok to use, although I prefer the reliability of Thunderbolt. HP Ice is very godd coverage, and due to the fact we are using Latios as a Steel killer, Magnezone can use a more uncommon Analytic variant. Use Stealth Rock if you use Banded Mamoswine, otherwise go with Volt Switch for the momentum. Thunder Wave is just awesome for crippling all sort of things.
That would be almost all, just a few things to beware about:
- At the moment, you lack a Rapid Spinner. Consider Donphan or Starmie instead of Heracross.
- Physical Walls such as Ferrothorn might cause you some trouble.
- Ground types are a potent, although not big threat.
That be all, good luck and happy hunting!
EDIT: By request, here are not 1 Rapid Spinner, but 2:
Starmie @ Life Orb
Trait: Natural Cure
EVs: 252 Spd/ 252 Satk/ 4 HP
- Rapid Spin
- Ice Beam
This is a replacement for Latios on your current team. The problem if you use it you becomes more troubled by Ghost and Dark types. To give you some option, here is another potent OU spinner:
Tentcruel @ Black Sludge
Trait: Rain Dish
EVs: 252 HP/ 252 Def/ 4 Sdef
- Rapid Spin
- Giga Drain
- Aqua Ring
Tenta have a similar problem to Starmie on this team, the team become exceedingly weak to Ground types, so I would suggest replacing Vicitini or Magnezone with Tenta to deal with that.