Gen 3 [is a RMT]

#1
Gengar (M) @ Leftovers
Trait: Levitate
EVs: 76 HP / 180 Spd / 252 SAtk
Modest Nature (+SAtk, -Atk)
- Hypnosis
- Ice Punch
- Thunderbolt
- Will-O-Wisp

EVs are probably royaly screwed.

Ludicolo (M) @ Leftovers
Trait: Swift Swim
EVs: 168 HP / 88 Spd / 252 SAtk
Modest Nature (+SAtk, -Atk)
- Ice Beam
- Leech Seed
- Rain Dance
- Surf

"sweep". stops Pert, which otherwise is a pain for this team.

Metagross @ Choice Band
Trait: Clear Body
EVs: 132 HP / 252 Atk / 124 Spd
Adamant Nature (+Atk, -SAtk)
- Earthquake
- Explosion
- Meteor Mash
- Rock Slide

a monster.

Blissey (F) @ Leftovers
Trait: Natural Cure
EVs: 212 HP / 252 Def / 44 SAtk
Bold Nature (+Def, -Atk)
- Ice Beam
- Protect
- Seismic Toss
- Wish

wish support and special wall.

Forretress (M) @ Leftovers
Trait: Sturdy
EVs: 252 HP / 192 Def / 64 SDef
Impish Nature (+Def, -SAtk)
- Earthquake
- Hidden Power [Bug]
- Rapid Spin
- Spikes

spikes. HP Bug is for celebi.

Swampert (M) @ Leftovers
Trait: Torrent
EVs: 240 HP / 20 Atk / 172 Def / 76 SAtk
Sassy Nature (+SDef, -Spd)
- Earthquake
- Ice Beam
- Rest
- Sleep Talk

yea.
 
#2
You've got a lot of ice attacks (4/6 of your team is carrying Ice Beam or Ice Punch). Since Blissey learns Flamethrower, Bolt, and Ice Beam, you may want to experiment with each of those attacks as you'd still have Ice covered with literally half of your team.
 
#3
Gengar (M) @ Leftovers
Trait: Levitate
EVs: 76 HP / 180 Spd / 252 SAtk
Modest Nature (+SAtk, -Atk)
- Hypnosis
- Ice Punch
- Thunderbolt
- Will-O-Wisp

Go Hasty imo, to outrun more stuff, and because double status Gar wasn't really meant to sweep a lot. Consider Explosion>WoW/Hypno.

Ludicolo (M) @ Leftovers
Trait: Swift Swim
EVs: 168 HP / 88 Spd / 252 SAtk
Modest Nature (+SAtk, -Atk)
- Ice Beam
- Leech Seed
- Rain Dance
- Surf

Use Celebi instead? ._.

Metagross @ Choice Band
Trait: Clear Body
EVs: 132 HP / 252 Atk / 124 Spd
Adamant Nature (+Atk, -SAtk)
- Earthquake
- Explosion
- Meteor Mash
- Rock Slide

Blissey (F) @ Lum Berry
Trait: Natural Cure
EVs: 212 HP / 252 Def / 44 SAtk
Bold Nature (+Def, -Atk)
- Ice Beam
- Protect
- Seismic Toss
- Wish

Lefties imo.

Forretress (M) @ Leftovers
Trait: Sturdy
EVs: 252 HP / 192 Def / 64 SDef
Impish Nature (+Def, -SAtk)
- Earthquake
- Hidden Power [Bug]
- Rapid Spin
- Spikes

Some Atk wouldn't hurt.

Swampert (M) @ Leftovers
Trait: Torrent
EVs: 240 HP / 20 Atk / 172 Def / 76 SAtk
Sassy Nature (+SDef, -Spd)
- Earthquake
- Ice Beam
- Rest
- Sleep Talk

I prefer Relaxed. You don't really have a Rock weak, so why not Milo/Cune over this?
The team's pretty solid, I had to look it over around ~5 times to find weaks (or maybe it's cause I suck =/ ) I can see Zappy giving you trouble, as it outstalls your Bliss, so that's another incentive to use Celebi over Ludi. You also lack a phazer, maybe give Pert Roar/Protect and make the Blissey a AT set?
 
#5
Swampert (M) @ Leftovers
Trait: Torrent
EVs: 240 HP / 20 Atk / 88 Def / 76 SAtk / 84 SDef
Relaxed Nature (+Def, -Spd)

Gives your Swampert 2 more def while the other stats are the same. I don't know much about EVs, though.