Gonna jump right in this. Off the bat I can tell you that the pokemon themselves are not that bad, but your items and moves are a bit off. Fear not, however, for no one is perfect and it's a landslide better than my first team was :)
Okay so recently I have been going through a Keldeo fetish, I just love the thing. I've been favoring an Ebelt set wired for coverage but Keldeo is also one of the best scarfers in OU. The only problem is, you are running physica Keldeo. Keldeo should always be a special attacker, as it's Special Attack is drastically higher than its Attack, and it's special movepool is dominant to it's physical movepool as well. This is the Scarf set I've been rocking in an OU team I made a few weeks ago and I must say I'm pleased with it.
Keldeo-R @ Choice Scarf
EVs: 4 HP / 252 SAtk / 252 Spd
- Hydro Pump
- Icy Wind
- Hidden Power [Ghost]
- Secret Sword
Hydro Pump is your water STAB and has a very satisfying ability to dish out immense volumes of power. Icy Wind's ability to lower the speed of an enemy is a large niche for my Ebelt set, but since this is a scarfed variant, the lowering of the speed rarely makes a difference, but the coverage does. It serves as a reliable way to get rid of Landorus in case you don't want to miss Hydro Pump, and is instrumental in allowing Keldeo to squish Dragon types which otherwise wall it. Another perk to Icy Wind is that it allows Keldeo to run Hidden Power Ghost, which brings down Psychic types such as Alakazam, and stops it from being completely shut down by Jellicent. Secret Sword is secondary STAB and is pretty much a fighting type Psyshock with a small power increase, which is very important for smashing Blissey and other special walls, while still hitting reliably hard.
K, so I originally had replaced this dude for Ebelt Jolteon (I <3 Ebelt) but after I thought about it the team can handle the Ice and I'll be replacing Volcarona so you needn't worry about rock too much. I will be improving upon your set, however.
Thundurus-T @ Life Orb
Trait: Volt Absorb
EVs: 252 SAtk / 4 Def / 252 Spd
- Hidden Power [Ice]
- Focus Blast
So this is the standard Agility sweeper set for Thundurus and despite it's fear of Ice Shard, if it can get an Agility up it is quite hard to bring down. Agility lets it run Modest nature, meaning you'll be at 427 SAtk completely unboosted, and that's something to brag about. After an Agility anything that would usually threaten you besides Priority can be forgotten about, and you can use STAB Thunderbolt to sweep, Hidden Power Ice to bring down ground and Dragon types, and Focus Blast to screw Rock and Ice types, as well as being Thundy's best move to put down Jolteon.
Breloom + Spore = Rage >:v
Breloom is such a beast it isn't even funny, but Effect Spore isn't allowing him to reach his full potential as a devasating sweeper, and neither is is item, the Razor Claw.
Breloom @ Leftovers/Life Orb
EVs: 4 HP / 252 Atk / 252 Spd
- Mach Punch
- Bullet Seed
- Swords Dance/Low Sweep
Rather straight forward. Spore leaves no excuse for the opposing pokemon to not get their beauty sleep, Mach Punch is STAB priority and boosted by Technician, Bullet Seed is STAB and also boosted by Technician, while your last slot is between whether you want a sweeper that will be able to come in a lot and hit stuff hard (Low Sweep), or a sweeper that is terrifying to face but prone to revenge killing (Swords Dance). If you go Low Sweep, run Life Orb, if you go SD, run Lefties.
I kind of like the idea of having an insanely bulky pivot amidst an offensive team, but I am going to replace Blissey with Chansey, as Chansey is bulky from both the physical and special spectrums.
Chansey @ Eviolite
Trait: Natural Cure
EVs: 252 HP / 252 Def / 4 SDef
- Stealth Rock
- Seismic Toss/Toxic
This thing will serve a similar role as Blissey, but will be bulkier overall and is not the Queen of England from the physical side, as Blissey is. Wish and Protect allows Chansey to pass Wishes like a boss, supporting you team mates a lot, and Chansey needs it to, as it loses Leftovers due to the Eviolite. Stealth Rock is another way Chansey can support your team, as Rocks can potentially shut down some very large threats such as Volcarona, Dragonite, and Ninetales. Your last movslot is whether you want to be able to Toxic stall and be taunt bait, or not be able to deal crap to anything but not be Taunt Bait. Honestly most pokemon that carry Taunt are ghost types so Seismic Toss won't do squat anyway, and Taunt is quite rare for some reason, so I recommend Toxic, but if Taunt becomes troublesome, switch over to Seismic Toss.
This thing is a complete momnster. Quite bulky, able to run a plethora of sets, and with a very nice SAtk stat. I will be suggesting a bulky attacker set that can take hits, spread burns, and retaliate with decent force. I've faithfully used this set since I got it off of Smogon about 6-7 months ago and I still use it even since it's been taken off the Rotom-W page becaue it still works
Rotom-W @ Leftovers
EVs: 184 HP / 148 SAtk / 176 Spd
- Hydro Pump
- Volt Switch
- Pain Split
Hydro Pump is your main STAB, Volt Switch is for safely switching into another sweeper of yours and dealing damage, Will-O burns enemies increasing the overall bulk of the team, and Pain Split is the best Rotom can do for a recovery move.
Volcarona is great but he doesn't synergize exceptionally well with the team and he throws off your Physical/Special balance, so I will be suggesting a different bug type. Scizor. A CB set should suit the team well as a trapper, revenge killer, and pivot.
Scizor @ Choice Band
EVs: 252 HP / 252 Atk / 4 SDef
- Bullet Punch
Standard CB Scizor. Bullet Punch is STAB priority, Superpower is coverage against Heatran, Magnezone, and other Steel types, Pursuit traps things such as Celebi and the Lati twins, and U-turn hits like a bomb, while gaining momentum.