Mimikyu can be found rarely in the Thrifty Megamart (Abandoned Site) after defeating the Totem Mimikyu in Acerola's trial.
Move over, Togedemaru - Mimikyu is the best Pikaclone in Generation 7! Although it is absurdly hard to find, having a 5% encounter rate in one location, it is not impossible. If you do get your hands on a Mimikyu, get ready to use one of the best physical sweepers in the game. With a free damage soaker under the name of Disguise, access to powerful STAB and non-STAB attacks, many setup options, and speed that renders much of Alola to its knees, Mimikyu is easily one of the best Pokemon to attain in a Nuzlocke through the Alola region.
Plumeria (Route 15): Set up Swords Dance on turn 1 before Golbat breaks your disguise, and you will be able to 2HKO with Shadow Claw. Salazzle might be a bit more dangerous, however - its Flame Burst 3HKOs, not counting any extra damage you may have taken against Golbat, and it will outspeed, while your Shadow Claw only 2HKOs with the Swords Dance. With enough health left, however, you should be fine.
Guzma (Shady House): Golisopod may prove to be a bit tricky to battle one-on-one, but it is manageable if you set up Swords Dance on turn 1. After two +2 Shadow Claws, Emergency Exit will be triggered. The best part about it is that once Golisopod comes back in, it will be within range for a KO, because Mimikyu's +2 Shadow Claw is a 3HKO without the ability. The trickier part of the fight is, surprisingly, Ariados. Although Shadow Claw 2HKOs at +2, Ariados is likely to spam priority attacks, which can 4HKO, which is dangerous if Golisopod did manage to injure Mimikyu.
Gladion (Aether House): Swords Dance on turn 1, and Shadow Claw will 2HKO Golbat - just be careful, as Acrobatics can take out half of Mimikyu's HP once Disguise is down. Fortunately, that HP can be restored, as Sneasel will be OHKOed using a +2 Leech Life, but be careful if you're injured from Golbat's attacks - Sneasel outspeeds and its Metal Claw can 3HKO. Finally, Type: Null is an easy target with Leech Life - it 3HKOs, while its Pursuit cannot do enough to nullify the health restoration from Leech Life.
Nanu (Malie City, Dark-type): This fight will prove to be a little dangerous, so take caution. Two Swords Dances are required to make this fight survivable. Mimikyu will OHKO Sableye using Shadow Claw after two Swords Dances, while Sableye can only break Disguise and do approximately half of Mimikyu's HP in damage. While that seems like a lot, it will be restored following the Krokorok which will be OHKOed by Leech Life after 2 Swords Dances and minus Intimidate. As for Persian, the best course of action would be to temporarily equip the Buginium Z to Mimikyu and use Savage Spinout against Persian in order to OHKO, as its Fur Coat ability allows it to survive one Leech Life and retaliate with a powerful Black Hole Eclipse.
Faba (Aether Paradise): Swords Dance turn 1, Shadow Claw to OHKO, be wary of Hypnosis. Y'know, Faba really needs a better party.
Faba (Aether Paradise, tag battle with Hau): Well, looks like Faba took the advice that you read literally 2 seconds ago - he actually has some more Pokemon now. Your first goal in this fight is to take out the Ledian, which can cause some grief with its screen setups. This can be done by Swords Dancing on turn one and hoping it uses Light Screen over Reflect. If it does use Reflect, use another Swords Dance, but be careful - Slowbro's Psychic can 3HKO after breaking Disguise, while Mimikyu can only 2HKO with a +2 Shadow Claw without the Reflect up. If you do get damaged taking out Ledian and Slowbro, Bruxish is fortunately OHKOed with +2 Leech Life (+4 if Reflect is up). Hypno is, once again, OHKOed by a +2 (or a Reflect and +4) Shadow Claw.
Guzma (Aether Paradise): Handle Golisopod the same way you did at Shady House - Swords Dance turn one, two Shadow Claws to trigger Emergency Exit, Shadow Claw to pick up the KO on the return. Shadow Claw will 2HKO Ariados, but once again, watch out for its priority attacks - both Shadow Sneak and Sucker Punch are 4HKOs. Shadow Claw 2HKOs Masquerain as well, but be careful if you've been weakened by the earlier fights, as Air Slash can 3HKO. Pinsir is a joke - it has one move that can hit you, and it is trash.
Lusamine (Aether Paradise): As long as Clefable only attacks once or twice, setting up 3 Swords Dances on if is a good idea right off the bat, as it allows you to OHKO Clefable (2HKO if it did decide to boost with Cosmic Power), although you should probably use a Hyper Potion to restore any lost HP before KOing. At +6, a lot of things are OHKOed by Shadow Claw, including Lilligant, Mismagius (although Mismagius outspeeds, and Shadow Ball can wipe 80% of your HP), and even Milotic. Bewear cannot touch Mimikyu at all, making it the safest part of the fight - just spam Leech Life and occasionally Swords Dance to remove the Attack reductions that Baby-Doll Eyes does.
Hapu (Vast Poni Canyon, Ground-type): Shadow Claw will OHKO Dugtrio after a Swords Dance, but be careful - Iron Head can take 90% of Mimikyu's HP away, and Sandstorm will make things a hassle later on, so be careful! Gastrodon is 2HKOed by that +2 Shadow Claw, but make sure you heal up before attacking if you got hit by that Iron Head. Flygon is super easy - if you leveled up to 46 before this fight, which you really should have, you'll have Play Rough, which OHKOs after a Swords Dance. Finally, Mudsdale is a monster. Stay away from it, elsewise you'll be taking a Tectonic Rage and/or Heavy Slam to the cloth-face.
Totem Kommo-o (Vast Poni Canyon): You got Fairium Z immediately before the fight. You leveled up to the point of getting Play Rough before fighting Hapu. Use Twinkle Tackle to score an OHKO against the Totem before it summons something like Scizor.
Lusamine (Ultra Space): Prepare yourself for a fun fight. The first thing to do is set up Swords Dance 3 times and hope that Clefable doesn't cause too much damage with Moonblast/get a powerful attack with Metronome. Once Clefable goes down, it's essentially a mirror of the previous bout with Lusamine - OHKO Lilligant with Leech Life, Mismagius with Shadow Claw (once again, be wary of Mismagius' Shadow Ball), and Milotic with Shadow Claw. Bewear is, once again, completely and utterly walled by Mimikyu - use Play Rough to win.
Solgaleo (Altar of the Sunne, Sun only): Steel-type move that can OHKO through the disguise? No, thank you.
Lunala (Altar of the Moone, Moon only): Ghost-type move that can OHKO through the disguise? No, thank you.
Gladion (Mount Lanakila): Keep away from Crobat - although your Swords Dance-boosted Shadow Claw will 2HKO, it outspeeds, and since you're spending a turn using Swords Dance, it can break your disguise and 2HKO with Acrobatics. Weavile is an easy enough kill - OHKO with +2 Leech Life. Stay away from Lucario - Corkscrew Crash will OHKO. Silvally is also a little terrifying in any of its formes - its Multi-Attack has a chance to 2HKO, and there is a chance that it can outspeed you, so keep back.
Hau (Mount Lanakila): Hau's Raichu can be OHKOed without a Swords Dance boost, but because it'll make the rest of the battle easier, it's recommended to do so first. Komala is another simple target to kill, with a likely OHKO on +2 Play Rough, although be careful if it misses - Komala's Shadow Claw will 2HKO. Flareon is 2HKOed by Shadow Claw, but Flare Blitz can wipe out 75% of Mimikyu's health, so watch out. Play Rough 2HKOs Vaporeon, making it a fairly safe target. Leech Life will 2HKO Leafeon, so go wild with that move - at least you get some recovery. Primarina is 2HKOed by Play Rough, but be absolutely careful - Primarina's Hydro Vortex has a small chance to OHKO. Decidueye is the easiest of the bunch, being OHKOed by +2 Shadow Claw before it even has a chance to launch a Bloom Doom. It's probably a good idea to stay away from Incineroar though - an Inferno Overdrive coming off of its Flare Blitz will hurt a lot if you don't have Disguise activated.
Elite Four Hala (Pokémon League, Fighting-type): As per the usual, set up a Sword Dance against Hariyama as it breaks your Disguise. Once that is done, everything will be OHKOed by Play Rough, except for Bewear. However, using a Fairium Z and Twinkle Tackle will remedy that situation, making this a clean sweep. Alternatively, you can use two Swords Dances to start the fight, which will have essentially the same effect except now Bewear is also OHKOed by Play Rough.
Elite Four Olivia (Pokémon League, Rock-type): This fight is much trickier than Hala, purely because of the high defenses of her Pokemon. That, in conjunction with her Carbink's Reflect, create a challenge. If you decided to reteach Wood Hammer at the Lanakila Pokemon Center before the league, though, this fight becomes what every other fight has been: One Swords Dance to sweep everything through an OHKO that doesn't have Sturdy or is not Probopass, which is 2HKOed. However, if you do decide to go with Wood Hammer, Mimikyu will require a lot of maintenance to keep its health up. As such, it might be a good idea to keep away from this fight.
Elite Four Acerola (Pokémon League, Ghost-type): You have a type advantage here in the form of Shadow Claw, but so do her Pokemon, meaning that you must take out everything immediately or risk being taken out yourself. Use the Disguise turn to set up Swords Dance against her Sableye, and if it uses Confuse Ray, take another turn to use a Full Heal, because you do not want to be left open for an attack after a confusion hit. After the Swords Dance is set up and you aren't confused, OHKO Sableye with Play Rough, because Shadow Claw doesn't quite pick up the kill. Once Sableye is knocked out, Shadow Claw will OHKO everything else, with the potential exception of Palossand, which only has a 50% chance to be OHKOed. Leaving Palossand open like this is the worst thing you can do, as its own Z-Move will OHKO Mimikyu. However, do not forget that you have a Ghostium Z as well - a Never-Ending Nightmare off of your Shadow Claw will be able to pick up the guaranteed OHKO that Shadow Claw doesn't have. One more word of warning: Acerola does have a Pokemon that outspeeds Mimikyu: Froslass. While it can't OHKO, a critical Shadow Ball will hurt.
Elite Four Kahili (Pokémon League, Flying-type): Skarmory is a dangerous target - you just don't have the offensive strength to break those defenses before it can use Steel Wing to 2HKO after Disguise is broken, so stay away. As for everything else, you may want to set up two or even three Swords Dances before beginning to fight. Crobat is bulkier than one would believe, requiring three Swords Dances for a guaranteed OHKO with Shadow Claw (although +4 still has a chance to OHKO). Oricorio will be OHKOed with a +4 Shadow Claw, and you outspeed it. Mandibuzz is the easiest part of this fight, being OHKOed by Play Rough after a single Swords Dance before it can even retaliate. Toucannon is a risky target thanks to Supersonic Skystrike, which will likely OHKO Mimikyu. However, a +4 Play Rough or a +2 Twinkle Tackle will be able to OHKO before Toucannon's Z-Move enters play.
Professor Kukui (Pokémon League): Lycanroc is a difficult target, as it outspeeds and can 2HKO with Stone Edge after your Disguise is busted, so it may be difficult to set up on this thing, let alone attack. Ninetales, on the other hand, is another story - it lacks the offensive strength to do anything more than 3HKO with Blizzard, allowing you to set up two Swords Dances. And yes, two boosts will be necessary to survive the fight. At +4, Play Rough will OHKO Braviary. Magnezone is terrifying when one gets right down to it, as Flash Cannon can take out 90% of Mimikyu's HP with a single Flash Cannon. However, you outspeed Magnezone and will be able to 2HKO with your +4 Shadow Claw, should you choose to risk it. Snorlax can be attacked by Mimikyu's Twinkle Tackle for a guaranteed OHKO, but if you don't have Fairium Z on Mimikyu, keep away from Snorlax - Heavy Slam can OHKO without a Defense-boosting nature or EV training. Decidueye is, unfortunately, trash against Mimikyu and can be OHKOed with +4 Shadow Claw. Stay away from Incineroar, as you aren't even guaranteed an OHKO with a +4 Play Rough, while its Inferno Overdrive off of Flare Blitz can OHKO. Primarina is OHKOed by a +4 Play Rough, but be careful if you're at low health from a prior fight, as Aqua Jet does cause a bit of damage and can pick you off if you choose to ignore it.
Tapu Koko (Ruins of Conflict): Mimikyu has done well, but Koko unfortunately beats it in raw strength - let a Mudsdale take care of it.
Post-Game: Mimikyu serves as an effective counter to many of the Ultra Beasts, with the potential exception of Nihilego. Go wild with it, but make sure you have a lot of Beast Balls.
After catching Mimikyu, it will know Shadow Sneak, Mimic, Feint Attack, and Charm, all of which will essentially be useless except for Shadow Sneak, which lets Mimikyu pick off weakened targets. However, if you're unfortunate enough to catch a Mimikyu at level 32 rather than a level 31 or lower one, Shadow Sneak will be knocked off of its moveset in favor of Slash. Yeah... Anyways, no worries - at level 37, Mimikyu learns Shadow Claw, which should immediately be put onto the moveset. Hone Claws is learned at level 41, which is pretty good, especially if you don't want to risk a Play Rough miss later on, although you have to use it twice to get the immediate Attack boost that Swords Dance grants. At level 46, you learn Play Rough, another necessity, as it is Mimikyu's only physical Fairy STAB (or rather, the only physical Fairy STAB at all). Finally, at level 50, skip out on Pain Split.
At Mount Lanakila, you may use the Move Relearner to teach Wood Hammer for a high BP attack at the cost of recoil, or Splash, for the arguable use of its respective Z-Move. On the TM front, Mimikyu learns two very good ones: Swords Dance, which vies for Hone Claws as Mimikyu's setup move, and Leech Life, which provides a very nice source of recovery. One may also find use in Return, which has very nice base power once you get your friendship up. Some status moves which you may potentially use, although are outclassed by other moveset options, include Thunder Wave, Toxic, Substitute, and Protect.
Mimikyu is a very nice user of Z-Moves. Shadow Claw and Ghostium Z creates a nice Never-Ending Nightmare, while Play Rough and Fairium Z provide a powerful Twinkle Tackle, which, coincidentally, is received immediately before the Totem Kommo-o. Savage Spinout from Leech Life and Buginium could also work, but is outclassed by Ghostium and Fairium. Finally, we reach the ultimate Z-Move debate: Z-Splash. A +3 Attack boost sounds very tempting at first glance, and in the right hands, can work to marvelous effect. However, you're sacrificing a potential nuke for a one-time Attack boost, resulting in a wasted moveslot if you're forced to switch, as well as another Pokemon's Z-Move usage for that battle. Personally, I would stick with Swords Dance, as it is much more reliable than Z-Splash proves to be.
Recommended moveset: Shadow Claw, Play Rough, Swords Dance / Hone Claws, Leech Life / Shadow Sneak / Wood Hammer
Fire-types: Fire-types have excellent synergy with Mimikyu, being able to take out Steel-type threats that Mimikyu cannot. Furthermore, Fire-types can take Steel-type attacks which would otherwise spell unfortunate doom for Mimikyu.
Defensive Pokémon: While Mimikyu can take that free hit thanks to disguise, its low HP means that once Disguise is down, Mimikyu won't last too long against other fast sweepers. As such, Mimikyu needs a bulkier Pokémon it can fall back on in case things go south.
Minimum stats are calculated with 0 EVs, IVs of 0, and a hindering nature, if applicable.
Maximum stats are calculated with 252 EVs, IVs of 31, and a helpful nature, if applicable.
What Nature do I want? Special Attack is useless on Mimikyu. If you can get an Attack or a Speed-boosting nature, such as Adamant or Jolly, prepare to win. A lot.
How good is Mimikyu in a Nuzlocke? The actual encountering of Mimikyu is the biggest hurdle one has to cross when attempting to use it. Once it is caught, the Alola region won't know what hit it. By following the simple order of Swords Dance and Attack, many trainers won't even know what hit them. In short, if you find a Mimikyu as your first encounter, use it - you will not regret it.