Let's see... Indeed, this team seriously needs work. First of all, I like how you use the six Water-type starters together, but that simply doesn't work well. First, Rotom-Mow poses a huge problem, and you have no, I mean, nothing to counter it. Swampert is easily smashed by Leaf Storm, while a combinaison of Leaf Storm and Thunderbolt repeatedly can sweep this team, and you can merely answer to it. That's why Feraligatr and Samurott have to go. I love them both, especially the latter, but they are outclassed, and their use is rather delicate. The former works with a Dragon Dance set, but you don't need three pure Water-type in a monotype, as the purpose of it is to focus on the second type. Samurott does well in NU, but nowhere else.
Google about natures and guide to good movesets, because yours are terrible. I mean no offense, though.
The team.
Empoleon @ Petaya Berry:
Trait: Torrent
EVs: 252 SAtk / 252 Speed / 4 SDef
Modest Nature
IVs: 30 HP
- Surf
- Ice Beam
- Substitute
- Agility
SubPetaya set. Agility will make you faster than you can think, even if you are at a low pace of 60 Base Speed. The point of this set is to make Surf more powerful than ever, with Torrent, STAB and Petaya. All of that makes the penguin able to 3HKO Blissey and 4HKO Chansey, the premier special wall ever. 30 IV in HP means that after three Substitute, Petaya will activate. With the help of rocks, Empoleon should feel easy to sweep.
Rotom-W @ Choice Scarf:
Trait: Levitate
EVs: 252 HP / 252 SDef / 4 SAtk
Calm Nature
- Trick
- Hydro Pump
- Volt Switch
- Will-O-Wisp
I use myself this genius set, and this set can cripple walls and support Pokémons, as well as slow physical behemoths, such as Conkeldurr. Trick will give out a nasty Choice Scarf, rendering walls and support Pokémons useless for the rest of the battle. Volt Switch allows a decent ability to revenge kill, although not the fastest, as well as gaining the momentum in a battle. As for Will-O-Wisp, it is here to make it up for the lack of EVs in Defense, as it will halve the attack of burned Pokémons. Hydro Pump is not comfortable to take, and is your secondary STAB. I wished Rotom-W learning Scald...
Swampert @ Leftovers:
Trait: Torrent
EVs: 240 HP / 252 Atk / 16 Def
Adamant Nature
- Waterfall
- Earthquake
- Stealth Rock
- Ice Punch / Hammer Arm
Offensive Swampert OHKOes offensive Roserade with Earthquake, so underestimate it not. The three first moves are very self-explanatory: The two first are STABS and coming at the huge attack of Swampert, they are not easy to take. As for Stealth Rock, it only helps your team at the sweeping role. Ice Punch and Hammer Arm are at a competition for the last slot. While it is amazing how Ice covers Grass for Water, which Swampert implores, Trick Room's abundance make Hammer Arm's speed loss more viable.
For your Greninja, Ice Beam > Scald and U-Turn > Extrasensory (while being optional) and you are fine. I think you got the point of it yourself: camouflage and attack.
Cloyster @ Focus Sash:
Trait: Skill Link
EVs: 172 Atk / 252 Speed / 84 SAtk
Naive Nature
- Shell Smash
- Icicle Spears
- Hydro Pump
- Rock Blast
Setup and Sweep. In gen 5, Cloyster was deadly. This gen, Cloyster is as deadly as before. It sets one Shell Smash, takes a hit with Sash and proceed to the sweep. Pretty simple.
Blastoise @ Blastoisite:
Trait: Mega Launcher
EVs: 252 SAtk / 252 HP / 4 SDef
Modest Nature
- Water Pulse
- Dark Pulse
- Rapid Spin
- Aura Sphere
Easy to use, yet deadly. Water Pulse is stronger than you can think with Mega Launcher, and the 20 % chances to confuse are nice. Dark Pulse is enhanced by Mega Launcher and Aura Sphere as well. Rapid Spin will get hazards away, which Cloyster would like to ask.
Hope this helps :)
~ Sincerely yours, Blitz of Justice.