dragonite marval scale@metronome safeguard,earthquake,DD,outrage evs in atk and spd
tyaniatar sandstorm@assault vest crunch,stone edge,earthquake,ice beam atk and spd
garcomp rough skin@megastone outrage,earthquake,dragon claw,fire blast evs in atk and spd
should I add rain dance+blizzard to dragonite?
[Dnite]
Metronome isn't so good on dragonite - he won't be surviving long enough against other dragons to attack more than once or twice (unless you set up with dd and sweep, in which case you can still do better). Try a Haban berry, life orb/expert belt, or maybe lum berry (for outrage confusion). I can see blizzard (just this once) so you can deal with dragons better, but rain dance doesn't do anything for you, and ice beam is more reliable if you think you'll miss. If you go with a special ice-type move you'll want SpAtk in your EVs. Personally I'd just go for using physical dragon type moves, but this is your fight.
Also, safeguard isn't going to help you. Other dragons will just attack rather than status. I don't think dragons DO status anyway.
[T-tar]
Just so we're clear t-tar isn't a dragon and he's slow. Slower than almost every single dragon you're likely to see so it'd be better for his EVs to be in health rather than speed.
[Chomp]
Garchomp is pretty quick for a dragon, but his mega form isn't. Honestly I think slapping a choice scarf on him and then using outrage over and over is your best bet.
[Others]
If you choose to not use mega chomp you can use mega abomasnow. He's slow as dirt and most fire moves will wreck him, but if you get him in on a dragon that can't use fire (like haxorus) he'll definitely get at least 1 kill with a blizzard.
Azumarill is probably one of the best fairy-types available, and mega gardevoir can also fill in your mega spot and put in work doing it.
Greninja OHKOs a lot of frail dragon types, and rotom-W burns them (watch out for haxorus/kyurem-b though. They have abilities that negate levitate and can use ground moves on him).
Just my two cents, and I second Shadow's suggestion of Noivern. Didn't think of him until I peeked at his post.
I disagree on Goodra, unless you're really committed to using purely dragon types, but even then you might want to try Mence over our lord and master - he's soo slow.