Lucario

The last three POTW's have been UU and NU, so from reviewing Delcatty to Lucario is a HUGE difference, and considering that Lucario is one of the most impressive sweepers in OU, is not something to be taken lightly. Having Amazing special and physical attack already gives you a hint, but the decent speed, priority attacks, and its amazing typing it's no wonder he's such a beast. Through and through, Lucario is going to stay in OU for along time, and will remain a beastly OU sweeper for years to come.

Beast-Cario
Ability: Steadfast
Item: Life Orb
Adamant/Jolly Nature
252 atk 252 spd 4 hp
-Swords Dance
-Close Combat
-Extremespeed
-Crunch/Stone Edge
What a Beast, so much attack already, and he can get it higher, plus with his great typing, he gets a lot of switch in's, making this sweeper very deadly. Simple, simple, simple, come in on something non scary, set up a SD and continue to rip the opponent's team to shreds. Swords dance puts you attack into a great 700-800 zone, which is epic, regardless of nature. Close Combat, although lowering your defense, and special defense, is very powerful, and has STAB, and will murder anything slower than you. Extreme speed makes up for your okay speed, and gives you a priority for anything faster than you. Crunch deals with ghosts, which are immune to fighting and normal attacks. While Stone edge is amazing coverage with close combat, but you might not be able to KO, more defensive ghosts, like Dusknoir. The ability is useful, as if they do get you to flinch, they'll obviously be faster, and with Steadfast +1 speed, now you can KO them, and your faster now. The item gives you as much attack as possible, and although you will be losing HP, the attack boost is very welcome. Adamant gives you an amazing attack stat, and even amazingER with an SD up, and with extremespeed you speed doesn't really matter. But, Jolly gives you more KO's with close combat and crunch/stone edge, because you might be faster. The ev's are obvious for a sweeper.

Specario
Ability: Inner Focus
Item: Choice Specs
Modest/Timid Nature
252 sp atk 252 spd 4 hp
-Aura Sphere
-Vacuum Wave
-Shadow Ball/Dark Pulse
-Hidden Power Ice/Dragon Pulse
Now this set may not be AS scary as the set above, but it has surprise factor, and is very powerful, and still manages to have a priority attack. Since stealth rock is not an issue, you can have many switch ins, get in a powerful attack, and than switch out. Aura Sphere is a powerful move, and has STAB, and is a great powerhouse attack. Vacuum Wave has priority and STAB, and will KO those pesky pokes trying to be faster than you. Shadow Ball or Dark Pulse, are just for taking out ghosts, and pretty much either are usable. Hidden Power Ice works for countering dragons, grounds, and other sweeping machines like Salamence. Dragon Pulse gives you more coverage, but you might miss out on some KO's where you would get with Hidden Power. The ability makes you not flinch, which is useful. The item is obvious, as it makes this set scary. The nature again, is for speed with timid or special attack with modest, keep in mind that you will be switching in and out, plus you have a priority attack, so modest is favorable. The Ev's maximize speed and attack, which is obvious for a choiced pokemon.

Anti-LeadCario
Ability: Inner Focus
Item: Focus Sash
Adamant Nature
252 atk 252 spd 4 hp
-Counter
-Magic Coat/Toxic/Crunch
-Extemespeed
-Close Combat
Lucario is not the best at countering every single lead in the game, but with his priority attack, good STAB, counter, and a gimmick make him an excellent anti lead. Counter works well with focus sash, obviously, and gets you easy KO's on unaware opponents. Magic Coat is good for pokes like Roserade or Gengar trying to sleep you, and makes the whole anti lead thing obvious. Toxic is for bulkier leads that you can't KO, like Swampert, who will not appreciate being poisoned. Crunch is for anything that resists normal.fighting like ghosts. Close Combat is STAB, and very powerful, which brings us to Extreme speed, which will KO, usually, after close combat, and has priority. Focus Sash is obvious for protection, and for Counter. Adamant nature gives you as much attack as possible. And the ev's are simple for a sweeping anti lead. Inner Focus allows fake out users to get smacked with Close Combat, then Extremespeed KO them.

Lucario is just a beast, as you should notice considering, all of my sets are sweeper related. He does need some help though. Lucario on all of his sets, except the lead set appreciate stealth rock/spikes support. Lucario really likes a lure, like tyranitar, to KO his counters. Most importantly, Lucario is not a defensive pokemon, so a stall team doesn'twork with him, so make sue your team is hard hitting. Lucario's counters are pretty much, ghosts, and really bulky pokemon that can take a hit and deal one out.