Overview
Medicham has low base Attack and Sp. Attack, but it can run physical sets thanks to Pure Power, which doubles its Attack. So, that 240 max Attack (with no items, of course) raises to a TERRIFYING 480, even more than Rampardos (471), and is only surpassed by Black Kyurem's 482 (not a great difference, anyway) and Deoxys Attack Forme's 504. So... Gallade? Hahaha. Only 383 max Attack. And the same Speed (284 max). But Oh! Swords Dance, what Medicham lacks! But Oh! Stronger STAB moves! But... STOP, you two! Let's get going.
Medichampion (come on, someone will have a better pun)
-Psycho Cut (egg move)
-Hi Jump Kick/Drain Punch (egg move or tutor, I recommend this)
-Ice Punch (relearner or tutor, I recommend this)/Thunderpunch (relearner or tutor)
-Bulk Up (TM, and no, it can't learn Swords Dance)
Adamant or Jolly
Pure Power
252 Atk 252 Spd 4 HP
Choice Scarf or Band unless you run Meditate, then it could be... Muscle Band
With a Bulk Up and Muscle Band, Medicham overcomes Attack Deoxys. Bulk Up also raises Defense, then you may take a physical hit, so it's better than Meditate. Then, STAB moves. Psycho Cut is the first one. Hi Jump Kick has crazy power but may hurt you, so there's Drain Punch, so that if you get hit by an opponent you can recover. I would choose Drain Punch, with an already high Attack. Ice or Thunder Punch... The idea is hitting Flying-types hard, but I would go with Ice Punch (Dragons are one big problem often). However, you may think bulky waters are the problem, then... It's up to you.
Endu... No, just Reversal
-Reversal
-Psycho Cut
-Ice or Thunder Punch/Return (TM)/Feint
-Meditate
Focus Sash
Pure Power
252 Atk, 252 Spd and Nothing else
Lonely, Naughty, Hasty or Naive
Seriously, it can't learn Endure. Meditate because Bulk Up may make you not get to 1 HP (the idea there) by raising Defense. Because of the same, I let out th 4 HP EV's. Meditate until you get hit. Then your Reversal becomes CRAZY, and even more with STAB. Psycho Cut is the Psychic STAB. Ice or Thunder Punch will rid you of Flying-types, but Return hits hard everything except Rocks and Steels, which are gone with Reversal. Or run Feint, as it gets the same priority as Extremespeed, so you can use it if you need to quickly hit something that outspeeds you. But then Ghosts can give a hard time.
Countering Medicham
Physical Walls may do, but will still get hurt. Skarmory will do well as long as Medicham doesn't know Thunderpunch. Zoroark can disguise smartly and take Medicham out with Night Daze. Spiritomb shuts the Reversal set down if Medicham runs Return or Feint. Crobat and Staraptor outfly Medicham and can hit it hard with Brave Bird. Staraptor can also defeat Reversal users with Quick Attack... As long as it can take Feint after Brave Bird's recoil. Oh, that. Like always, priority ruins the Reversal set, but watch out for Feint. Extremespeed users that outspeed Medicham don't need to care, though. Special Attacks on the Bulk Up set do very well. Alakazam can use Shadow Ball, again, Zoroark's Night Daze, Volcarona's Bug Buzz, Espeon's Signal Beam... And hitting Reversal users without damaging them too much (not very effective moves) is useful if you can achieve it. Basically, if you can outspeed Medicham and OHKO it, you'll be safe.