Pokemon Black Version In-Game Team (need suggestions)

[ReclusiveDemon]

;130; Gyarados
-Dragon Dance
-Waterfall
-Earthquake
-Stone Edge

;376; Metagross
-Meteor Mash
-Zen Headbutt
-Hammer Arm
-Bullet Punch

:635: Hydreigon
-Dragon Pulse
-Crunch
-Flamethrower
-Surf

:637: Volcarona
-Quiver Dance
-Flamethrower
-Bug Buzz
-Psychic

This is my team for post-game, whether to beat up Cynthia, the Elite Four, etc.

I'm looking for a fifth and sixth team member. I think I need an Electric or Grass-type, since they have good synergy with the rest of the team, and it would be useful for destroying Water-types.

 

[! Q]

Rather than dip deeper into the sub-par Speed of Metagross by using Hammer Arm, I would rocket my way out with Agility. And if you have Agility, you don't really need the weak priority, so I'd replace Bullet Punch with Earthquake.

I'd replace your Flamethrowers with Fire Blasts. 85% accuracy is (by my standards) very reliable.

And, just for the raw awesomeness, replace Psychic with Hurricane. Sure it's an accuracy loss, but Hurricane. (And Psychic doesn't really provide much useful coverage.)

For the Grass type, I'd say a Technician Breloom. Abusing priority is fun, and you get the ever-useful coverage provided by Fighting types.

For the Electric type, go with... Eelektross? I dunno, having no weakness is cool. (I'm not really a fan of any particular Electric type.)

 

[Sohryu]

Flamethrower > Fire Blast because of accuracy. Although 85% is actually kinda fine, he's running a Quiver set, which is already providing the so needed power. The accuracy loss, in that case, is not needed. Specially in-game. And Hurricane is simply... Unnecessary. He can go without it, not to mention he have to train his Volcarona up to LV 90 to have it. And again, it is for in-game purposes. He's better going with Giga Drain to hit Water and Ground types, not to mention those pesky Rock types.
If you can, slap a Ice Punch on 'Gross ans take Hammer Arm out. The loss in speed is inconvenient in most situations. Earthquake, Iron Head, Ice Punch and Agility is probably a best bet, or you can keep Bullet Punch for priority instead of adding Agility.
A nice Eletric Type would be a Magnezone to take care of pesky Water-types. For Grass types... Nice question. Grass-Types aren't usually needed and I don't see a reason to have one. But since you're asking for it, Rotom-C is a nice addition. It adds some bulk to your team, and its dual type may be handy. It will add some MAJOR weakness to Fire, but it's your best bet (outside of Breelom, as well suggested by ! Q ).
Rotom-C should have: Leaf Storm, Thunder Bolt, Shadow Ball and Hidden Power - Fire if you can or Will-O-Wisp. This set does some major damage to Water Types. Either go with TB for reliability or LS for raw power, usually when you're facing bulky Water pokemons. Grass + Eletric while not the best STABs, there's some synergy with coverage. Shadow Ball is useless, but will come in handy when facing Chandelure. Hidden Power Fire will help to deal with Steel or Grass types that will probably be a problem. If you're not up to breeding, then go with WoW for some team support. Just make sure you won't be facing ANY Steel and Grass types. But really... Magnezone and Breelom is probably a better idea (as Rotom-C doesn't have a superb movepool).
All the best, Ark!