YES. FINALLY.
Mienshao is a total Boss, able to sweep through weakened teams without any boosts. It has base 105 speed, which out-speeds notable threats such Hydreigon, Haxorus, the vast base 100 speed tier, Garchomp, Landorus, and Zoroark. It unfortunately misses out on the other Genies, Infernape, Starmie, Gengar, Espeon, and the Musketeers Trio, but it's still fast. It has an amazing ability in Regenerator, allowing it to recover 1/3 of its health whenever it switches out, which pairs incredibly with U-Turn and Life Orb, and makes a HJK miss less crippling.
Fake Out Abuse
Mienshao @ Life Orb
Regenerator
Naive (+Spe -SpDef)/Jolly (+Spe -SpAtk) Nature
- Fake Out
- Hi Jump Kick
- U-Turn/Substitute
- Hidden Power Ice/Stone Edge/Taunt
Life Orb Fake Out really packs a punch, and since it now has +3 Priority, only Protect will let something dodge it. Hi Jump Kick is Mienshao's strongest move, with 195 base power after STAB. It hits incredibly hard, doing a minimum of 46% to Max/Max Skarmory, and hitting harder than Garchomp's Outrage. U-turn lets you get off a hit and get out of there, activating Regenerator as you go. Hidden Power Ice is really Mienshao's only way to touch Gliscor, and it will OHKO if Gliscor switches into a HJK first. However, if Gliscor isn't a problem to you, you can run Stone Edge to get physical coverage on Flying-types and run a Jolly Nature. On the other hand, give it Taunt, and it can function as an offensive anti-lead. Substitute lets Mienshao scout switches, or set up on Protects, that many people will try to use against Fake Out and Hi Jump Kick, leaving them in a bit of a predicament. Not many things can either take two hits from Mienshao or take one and out-speed it.
Choice
Mienshao @ Choice Scarf/Choice Band
Regenerator
Naive (+Spe -SpDef)/Jolly (+Spe -SpAtk) Nature
-Hi Jump Kick
-U-Turn
-Stone Edge
-Hidden Power Ice/Drain Punch
Mienshao can make an incredibly powerful Choice user. Regenerator is an ideal ability for a choice user, which generally needs to switch out a lot. With a Choice Scarf, it out-speeds pretty much the entire metagame, letting it work as a powerful revenge killer, and with a Choice Band, it hits incredibly hard with Hi Jump Kick. U-turn lets you keep momentum, scouting switches, Stone Edge destroys flyers, and Hidden Power Ice hits Gliscor. Drain Punch is another option, letting Mienshao recover some of its health without switching out, and is more reliable than Hi Jump Kick.
Comments/Additional Options
Team Preview is a blessing to Mienshao, because it lets you scout and see if your opponent has any Ghost-Types that they might switch in on your Hi Jump Kick to try and get a free 50% hit on you. Mienshao has the ability to run a special set, getting access to Aura Sphere, but its Special movepool is a little sparse, and it is outclassed by Lucario, which has a much higher special attack. Mienshao is the fastest user of Me First, and is the only one that is faster than the many Dragon-types, and paired with Substitute or Taunt, which forces your opponent to attack, it could form a potent combination. Mienshao gets both Swords Dance and Work Up, so a boosting set could be viable, but it doesn't really have the coverage to sweep effectively, and is in many occasions too frail to set up.
Counters
Jellicent hard counters Mienshao, especially those with HP Ice, but even Stone Edge is only a 3HKO, and Jellicent can stall it out with Will-O-Wisp and Recover.
Gliscor also hard counters Mienshao, but only if it lacks HP Ice.
Anything that outspeeds Mienshao (Tornadus, Thundurus, Infernape, Starmie, Gengar, Musketeers, Espeon) can OHKO it. It really is incredibly frail.
Gyarados and Zapdos can deal with Stone Edge-lacking variants.
Anything with Protect, or Ghost-types can potentially cause Hi Jump Kick to backfire.
Teammates
Mienshao needs something that can take care of those faster threats mentioned before. Scarfed Garchomp or Terrakion work well. Something to deal with Jellicent is necessary. Powerful ghost, electric, grass or dark-types work well. Entry hazards make Mienshao's life easier, as it misses out on a few OHKO's by only 3-5%.