Rate My Team =)

Adamant Metagross @ Lum Berry
Clear Body Ability
252 HP / 236 Atk / 12 Def / 8 Spe
~ Agility
~ Meteor Mash
~ Earthquake
~ Explosion

Timid Froslass @ Focus Sash
4 Def / 252 SpA / 252 Spe
~ Spikes
~ Taunt
~ Destiny Bond
~ Ice Beam
Froslass uses Destiny Bond and Focus Sash to a sin it's foes =)

Modest Drifblim @ Leftovers
Unburden Ability
144 Def / 252 SpA / 60 SpD / 52 Spe
~ Calm Mind
~ Shadow Ball
~ Thunderbolt
~ Hypnosis

This Bad Boy abuses Leftovers and Unburden to speed above the rest. It uses this speed to hypnotize the foes, and calm mind while they're down. Or, kill them while they're low =P

Jolly Swellow @ Flame Orb
252 Atk / 4 SpD / 252 Spe
~ Facade
~ Brave Bird
~ U-Turn
~ Quick Attack

Flame Orb + Guts Ability + STAB = 257 BP Facade. Brave Bird + STAB = 150 BP Brave Bird. Quick Attack + STAB = 50 BP + Attacking With Priority. This dude can be one pain in the donkey to the other team ^^

Modest Yanmega @ Peteya Berry
Speed Boost Ability
4 Def / 252 SpA / 252 Spe
~ Substitute
~ Bug Buzz
~ Air Slash
~ Hidden Power Ground

Calm Clefable @ Leftovers
Magic Guard Ability
252 HP / 252 SpD / 4 Spe
~ Thunder Wave
~ Softboiled
~ Seismic Toss
~ Light Screen

Use Froslass as your lead. But keep in mind that Froslass doesn't work too well in OU. And with the majority of Pokemon being Flying-type in OU, and ones with Levitate, Spikes isn't the best thing in the world. Still not a bad lead, though. Just watch out for ghosts and steels, as some of them carry Bullet Punch or Shadow Sneak, which will ruin you. Also, that Froslass requires really good prediction. It can phail if you use the wrong move even once.

You have a big electricity weakness. I'd say get rid of Drifblim for something else, preferably another physical sweeper with an electricity resistance/immunity. Firstly, Drifblim isn't much of a wall, or a special attacker. I've tried that exact same set, and it doesn't work well. SR, Gengar, Suicune, Tyranitar and even Salamence to an extent, ruin Drifblim's day. Secondly, it's too slow to really do anything. You're likely to get hit first, and from there, you have to pray to God that Hypnosis hits. Otherwise, you die the next turn. In spite of its high HP, it takes heavy damage from many neutral attacks. If you must keep Drifblim, get rid of Unburden for Aftermath, and give it a Wide Lens. But I'd just say ditch it.

There's a lot of stuff you can do with Clefable, but that set doesn't seem to do as much as it could. Your team is in need of a wall, so I would go with this:

Clefable@Leftovers
252 HP 212 Def 44 Sp Def
Cosmic Power
Softboiled
Seismic Toss
Shadow Ball

This Clefable is best used in conjunction with Hypnosis from Yanmega. Use CP as much as you can, recover any residual damage, and raise heck. I chose Shadow Ball because you would not be a happy camper if you just CP'ed up, then the opponent sends out Gengar or
another ghost-type, walling you completely. The EVs will help with fighting-type attackers, since those are the only real hope with Clefable, and 99% of Fighting-type attacks are physical. Clefable has no hope of outspeeding much, so don't bother with Speed.

The rest doesn't look too bad.