Okay, I must be insane answering TKOR's RMT, but anyway, let's try! :D
Note that Hypnosis has some shaky accuracy. If you miss, Politoed can easily get screwed over. You can replace it with Toxic to help land KO's more easily, but it's not necessary.
Dragon Dance is fun, isn't it? I'm getting the feeling that you're way too dependent on setting up. Quagsire would be laughing at you in the face. Well, I suggest you get rid of DD. Instead, a Choice Scarf set would work nice here; you get the Speed without the setup. It helps revenge kill easily.
Gyarados (M) @ Choice Scarf
EVs: 252 Atk / 4 Def / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Stone Edge
- Ice Fang
Waterfall is STAB boosted by the rain, Stone Edge and Earthquake form the infamous EdgeQuake coverage, and Ice Fang targets Dragons like Mence and D-Nite.
Okay, 3 things I'm going to say at first:
1. What's with the picture? A teddy bear with tentacles? xD
2. Double setup? Interesting.
3. Can I suggest Bulldoze? xD
Most unusual Ferrothorn you have here. I've seen Special Ferrothorn, Choice Band Ferrothorn, and other variants, but never this...
Anyway, I would just not go sweeping. I suggest this:
Ferrothorn (M) @ Leftovers
Trait: Iron Barbs
EVs: 252 HP / 88 Def / 168 SDef
Relaxed Nature (+Def, -Spd)
- Leech Seed
- Stealth Rock
- Spikes / Gyro Ball
- Power Whip
Too many sweepers in a team isn't too good. Besides, a hazard setter can help make KOs from your sweepers easier. Leech Seed saps HP from your opponent, and can heal Pokemon such as your Cofagrigus, who lack reliable recovery. Steatlth Rock breaks through Sashs from Cloyster and Dragonite's Mulitiscale. Spikes helps damage the opponent even more, or Gyro Ball hits Dragons that resist Power Whip. Power Whip is just a great STAB move overall.
I'd change the Nature here to Adamant. Waterfall can be used over Roost, but not really necessary. Also, if you're trying to go for a bulkier D-Nite, I'd suggest 252 HP / 44 Atk / 212 Spd.
My Jellicent will forever fear this guy.
You have WAY too many Physical Pokemon. Forretress and Skarmory can screw the team. Plus, you've got a huge Rock weakness by keeping Mence. I've got two options for the last slot-a mixed sweeper, and a Special sweeper. And they both resist Rock.
Jirachi @ Leftovers
Trait: Serene Grace
EVs: 248 HP / 8 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Calm Mind
- Psyshock / Water Pulse
SubCM! Substitute and Calm Mind....well, SubCM! Thunder abuses the rain and a 60% of paralysis occurs with Serene Grace. Psyshock is STAB, and Water Pulse is for Ground Pokemon and Tyranitar, mostly.
Virizion @ Life Orb
EVs: 104 Atk / 152 SAtk / 252 Spd
Hasty Nature (Spd, -Def)
- Work Up
- Giga Drain
- Hidden Power [Ice]
- Close Combat
Work Up boosts both offensive stats. Giga Drain is STAB and heals off Life Orb recoil. HP Ice hits stuff like Gliscor, Mence, D-Nite, Lati@s, and Landorus. Close Combat is STAB. Calm Mind sets work out too. 4 HP / 252 SAtk / 252 Spd with Timid, and Focus Blast over Close Combat.
I hoped I helped out.