Here are some competitive battling rejects I found to be pretty effective in UU:
Smeargle (M) @ Wide Lens
Ability: Own Tempo
EVs: 252 HP/6 Def/252 Spd
Jolly nature (+Spd, -SAtk)
- Spore
- Stun Spore
- Super Fang
- Stealth Rock
Double Spore. Spore the first turn, then Stun Spore on the switch, and you've already crippled 1/3 of the opponent's team. After that, you can Stealth Rock the opponent. Super Fang for damage, but you could also go for Night Shade, or Seismic Toss, too.
Chimecho (M) @ Leftovers
Ability: Levitate
EVs: 6 HP/252 Def/252 SDef
Bold nature (+Def, -Atk)
- Thunder Wave
- Recover
- Calm Mind
- Psychic
There's actually nothing special about this, just a UU rip-off of Latias, but still........Thunder Wave, Calm Mind, and heal damage. Psychic is for STAB, but you could put something else there for coverage.
Dodrio (M) @ Salac Berry
Ability: Early Bird
EVs: 252 Atk/252 Spd
Jolly nature (+Spd, -SAtk)
- Brave Bird
- Flail
- Endure
- Endeavor
With this, you Brave Bird for STAB and lower your health, and Endure if you think your opponent will finish you. Flail is there with it's massive 200 (full power) atk, plus STAB puts it at 300 power; as much as Explosion. Salace Berry to boost your speed and help the sweep, but Leichi works if you're feeling confident in your speed. But why do you need Endeavor if you have the amazing Flail? Well, things like Steelix and Registeel will wall you easily, so you just Endeavor them and revenge kill with someone else.
SubSalac fear set
Dodrio @ Salac Berry
Early Bird
252atk/ 252spd
Jolly
-Substitute
-Flail
-Quick Attack
-Endeavor
Dodrio has access to Quick Attack and Endeavor, making him just as annoying as any Rattata. By putting
no EVs in health and 31 IVs in it, Dodrio gets an uneven 261 hp, allowing him to sub 4 times and have 1 hp left. So you can Flail and sweep, and against a wall, you Endeavor and Quick Attack under the protection of sub. The difference between these two sets, is that the one above is more instant-sweep oriented. Again, berry is all about preference.
Linoone (M) @ Salac Berry
Ability: Gluttony
EVs: 6 HP/252 Atk/252 Spd
Jolly nature (+Spd, -SAtk)
- Belly Drum
- Extremespeed
- Flail
- Endure
Same idea here. If you manage to pull off a Belly Drum, then Gluttony activates Salac Berry earlier. Now, you can sweep with Extremespeed, or Endure+Flail. By Endure+Flail, you sweep with Flail and Extremespeed anything that might possibly be faster. Another option over Salac Berry, is Leftovers. That way, if you find you need to switch, you'd be at 56% hp after Belly Drum, allowing a 2nd Belly Drum.