Pokemon Diamond/Pearl Help

[mtjimmer]

I'd recommend having a variety of Pokemon, with a variety of attack types.
Uxie and Azelf are both Psychic-types. If one is a good match-up, so is the other. (Likewise, if they're a bad match-up, it's doubled.)

I really like Luxray, with its combination of Dark and Lightning attacks.
I'd recommend having some kind of Ice attack on one of your Pokemon...maybe add Ice Beam to your Empoleon's range of attacks. Ice is good against Grass-types and Dragon-types, both of which you don't have answers to.
Staraptor is good - Brave Bird and Close Combat give you strong Flying-type and Fighting-type moves. I used one in my first two teams. (I've been playing other games through as well, each time choosing Pokemon that I haven't used before...hopefully developing my skills and knowledge on Pokemon I previously considered less than perfect.)

 

[MegaVelocibot]

An often-underrated gem in Sinnoh is Octillery, the Remoraid evolution. If you don't mind its atrocious speed and somewhat lackluster HP, Defense, and Special Defense, get one that is Timid or Modest, or Jolly or Adamant.

If you go with the first two, load it up with Special Attacks. You'll discover it learns such gems as Psybeam, Aurora Beam, Bubblebeam, Octazooka (from the level Remoraid evolves into Octillery), Wring Out, Signal Beam, Ice Beam, and Hyper Beam. You can cover even more type basis with its Special compatible TMs and HMs: Blizzard, Brine, Charge Beam, Energy Ball, Fire Blast, Flamethrower, Flash Cannon, Hidden Power, Hyper Beam (don't wait the TM, it's a level up as well), Ice Beam (same), Mud Slap (just don't use this period), Psychic, Sludge Bomb, Surf, and Water Pulse.

The second two open up the door to Octillery's equally strong physical attack power, albeit with a far smaller move pool. Gunk Shot and Rock Blast are viable moves to be relearned, Bullet Seed from Level Up, and from TMs come Bullet Seed (level up, don't waste it), Facade, Frustration, Giga Impact (the physical Hyper Beam), Natural Gift, Payback (great for its slow speed and likelihood it will be hit first), Return, Secret Power, Thief (good for turning the Elite Four's berries against them if you go in with nothing on the Octillery, but not for damage), and Waterfall.

Status moves available include the crit-boosting Focus Energy from level-up, and TMs Attract (usable, since E4 don't like to switch out, but then you have to worry about genders, not recommended), Captivate (again, not recommended), Double Team (not liked against human players, but if it works, go for it. Just don't expect it to last long enough to reach max evasion), Endure (no real use), Protect (good if you get a status in on Flamethrower, Fire Blast, Gunk Shot, Psybeam, Secret Power, Signal Beam, Sludge Bomb, Swagger, Toxic or Water Pulse), Rest / Sleep Talk (kind of blah), Substitute (eh...), Swagger (the usual Swagger / Protect / Substitute combo, if you don't mind the gamble, but these HP, defenses and speed don't lead to a good use of it), Thunder Wave, and Toxic.

In general, you'll want Sniper over Suction Cups, for the boosted crit damage, which can, as mentioned before, be boosted by Focus Energy and the Scope Lens. With Scope Lens, Octillery will be able to score a Critical Hit in 1 out of 3 hits after using Focus Energy, which will deal triple damage instead of double due to Sniper.