How to Catch Mewtwo
Mewtwo in Generation One
If you head to Cerulean City and surf in the water beside Nugget Bridge, you will find a cave, known as Cerulean Cave (but often referred to by fans as the Unknown Dungeon). This cavern is filled with Pokémon so strong that, for safety reasons, the Pokémon League restricts access and only Pokémon Masters may enter. Once you obtain this coveted title, you may make your way through this labyrinthine cavern, and perhaps in its depths discover the strongest Pokémon of all: Mewtwo.
In this generation, most trainers would save their Master Balls for catching Mewtwo, in order to avoid the hassle of:
- Giving Mewtwo a status ailment, such as putting him to sleep, paralyzing, or freezing him
- Whittling Mewtwo's health down to next to nothing
- Not letting Mewtwo faint
- Not letting all their own Pokémon faint
- Using about a million Ultra Balls before achieving the great victory of catching him
With a Master Ball, you just:
- Confront Mewtwo
- Hurl the Master Ball at him
- You're done
For obvious reasons, using a Master Ball was the preferred method. Hence, Master Balls are closely associated with Mewtwo, and that is why I use little Master Balls as bullet points and such throughout the site. Nowadays, randomly appearing or so-called "running" Pokémon, such as the Legendary Beasts, are probably better candidates for the single Master Ball, since the Master Ball helps to alleviate the additional hassle of needing to chase them across the land and repeatedly getting lucky to even see them. But, back in the days of Generation I, the Master Ball was reserved for Mewtwo.
Mewtwo in Generation Two
In the Generation II games, the Unknown Dungeon is gone. I think the entrance caved in. Mewtwo was probably sick of being woken up in the middle of the night by pesky trainers trying to capture him, so instead, Mewtwo blocked the way into the cave with rocks. Or else, Mewtwo is no longer there at all, because Red captured him at the end of the Generation I games, which occurred chronologically three years before the events of the Generation II games.
Actually, the most likely reason there is no Unknown Dungeon in Generation II is for the boring real life technicalities of there simply not being enough room left in the cartridge. Game Freak crammed as much into the Generation II games as they could; they already had to cut the Safari Zone, the vast majority of the Seafoam Islands, and many other areas in Kanto to get everything to fit. The Unknown Dungeon probably wasn't ranked as a critical region that needed to be revisited in the sequel.
The only sign in Generation II that Mewtwo was ever in Cerulean Cave is a hidden trace of its DNA in the water: the Berserk Gene. The Berserk Gene is a held item, but I don't recommend actually using it. The Pokémon holding it gets boosted attack during battle, but suffers from confusion. The Berserk Gene is consumed after a single battle, and you only ever can get one, so using it is pretty pointless. It is so pointless that Game Freak didn't bother to include this item in any game ever again. It's probably better to treat it as just an Easter egg.
But anyway, whatever happened to the Unknown Dungeon, you can't catch Mewtwo in these games. The primary way to get Mewtwo in Generation II is to trade one up from a Generation I game using the Time Capsule.
Mewtwo was also available as a special event Pokémon in the Generation II era. The New York City Pokémon Center had special machines called Gotta Catch 'Em All Stations that visitors could use to get a random Pokemon traded into their game. From September 27 to October 3, 2002 and again February 14 to 20, 2003, a Shiny Mewtwo was available as a potential prize, from a pool that also included Shiny Venusaur, Shiny Charizard, and Shiny Blastoise. That's a cool way to get an official shiny Mewtwo, and would have been a fun souvenir from a trip to New York City!
Mewtwo in Generation Three
Mewtwo, like most other Kanto and Johto Pokémon, is not available in Ruby, Sapphire, or Emerald. On top of that, trading is impossible between these games and the earlier generations, so there is no possibility of trading up from the past. This means that when Ruby & Sapphire first came out, there was no way to have Mewtwo in a Generation III game!
Keep in mind that this was this first time anything like this had happened in the history of Pokémon. Game Freak had previously prioritized backwards-compatibility for all the games, even enabling two-way trades between Generation I and II games. Instead, the Generation III games created an impassible rift between the old and the new, and it didn't help that Generation III was being billed as a complete reboot of the series. At the time, I was outraged that I was expected to still love Pokémon, while being content to abandon and forget about all my old favorites, who seemed to be getting the axe in favor of pale imitations. Deoxys might be kinda like Mewtwo, but it can never replace Mewtwo in my heart.
It wasn't until more than a year later, with the release of FireRed & LeafGreen, that Mewtwo became obtainable in Generation III. Since these games are remakes of the Generation I games, Cerulean Cave is also present, and Mewtwo can once again be encountered there. If you catch this Mewtwo, you can trade him to any other game in this generation.
Mewtwo in Generation Four
In the HeartGold & SoulSilver versions, Cerulean Cave did not collapse like it did in the Generation II games these remakes are based on. I guess there is enough additional room available in the newer video game technologies that Game Freak was able to include the Unknown Dungeon this time around (which is now filled with strange blue-green crystals for some reason).
This retcon has some disturbing implications regarding the plot - this means that Red did not capture Mewtwo at the end of the Generation I games.
Timeline fracturing aside, Mewtwo can be captured in HeartGold or SoulSilver and then potentially traded to Diamond, Pearl, or Platinum, where Mewtwo is otherwise unavailable.
Alternatively, Mewtwo can also be transferred to Generation IV games from an older Generation III game using the Pal Park. So, you can transfer Mewtwo caught in Cerulean Cave in FireRed or LeafGreen to the newer games. When you do, Mewtwo will apparently appear in the Field area.
Mewtwo in Generation Five
An official event Mewtwo with a special moveset was available in Japan from September 26 to October 31, 2011 for Pokémon Black & White. A corresponding "Mighty Mewtwo" was available via Nintendo Wi-Fi Connection Mystery Gift for North America from February 10 to February 26, 2012 (Aw, how did they miss Mewtwo's birthday?) and gradually in other events around the world.
There was a different official event Mewtwo with a different special moveset for Black2 & White2 as part of the promotion of Genesect and the Legend Awakened on various dates in 2013 at special locations in Japan, Taiwan, Indonesia, and the Philippines.
Mewtwo can also be transferred to the Generation V games from a Generation IV game using Poké Transfer (so you can transfer up a Mewtwo caught in HeartGold or SoulSilver's Unknown Dungeon, or doubly transfer up a Mewtwo caught in FireRed or LeafGreen's Unknown Dungeon).
Mewtwo in Generation Six
It turns out the Unknown Dungeon is not only in Kanto, but there's a similarly Nameless Cavern in the Kalos region of Pokémon X & Y as well. And this cave has Mewtwo in it too! Maybe the Unknown Dungeon is so huge, it goes straight through the middle of the planet and has entrances on different continents? Except, unless we are not seeing some little crack in the wall, the cave in Kalos appears to be really tiny. Does the cavern's lack of a name come from the fact that Mewtwo is inside? Does Mewtwo like erasing people's memories so they forget the names of caves? Maybe it's a security measure so people leave him alone? Or maybe just for fun?
Anyway, this particular Unknown Dungeon looks to be extremely boring compared with its Kanto counterpart. There's apparently not much to it apart from Mewtwo just standing there, which honestly is a bit of a let down. I haven't played the game yet, but I've been told the entrance to the cave is located in a special Pokémon Village of hidden Pokémon, and despite this ripe scenario, Mewtwo actually has no plot-relevance at all. Aw man!
Well, at least after you catch him you can hand-feed him pastries and, uh, pretend that's not horribly demeaning to a sentient, intelligent super-psychic. Er...
Being remakes of Ruby & Sapphire, Mewtwo is not available in Omega Ruby & Alpha Sapphire except by trading. Mewtwo can also be transferred to the Generation VI games from a Generation V game using using PokéTransporter, so you can transfer up a Mewtwo obtained in Generation V's Mighty Mewtwo event or doubly transfer up a Mewtwo obtained in Generation IV's Unknown Dungeon, or triply transfer up a Mewtwo obtained in Generation III's Unknown Dungeon. So many Unknown Dungeons!
Additionally, for Generation VI games, a special event Shiny Mewtwo was distributed in Japan from April 28 to August 31, 2016, and also in connection with Pokémon World Championships events and Play! Pokémon events around the world.
Mewtwo in Generation Seven
Game Freak didn't bother to update Mewtwo's sprite - er - model for this generation, possibly because Mewtwo is not present in Pokémon Sun & Moon. However, Mewtwo can be obtained in the post-game of UltraSun & UltraMoon by exploring the so-called Ultra Space Wilds. In this part of the game, the player can access alternate dimensions and catch some Pokémon that aren't found in Alola. This includes many Legendary Pokémon, which are, apparently, not currently ruling their elements, protecting their domains, or sustaining their part of the cosmos, but instead are just trying to enjoy a vacation in this little pocket universe containing nothing but a disembodied beach in the voids of space-time. But the player has to come disrupt that, too, good job. Mewtwo might be found in the pocket universe accessed through the green wormholes, which the different Pokémon wikis have dubbed the "rocky" or "crag" world. Mewtwo will keep potentially respawning here until the player manages to catch one.
Being remakes of Pokémon Yellow crossed with Pokémon Go, the games Let's Go Pikachu & Let's Go Eevee once again have Mewtwo hiding in Cerulean Cave, and the crystals that appeared in HeartGold & SoulSilver are back and now glowing. After reaching Mewtwo's in the depths of the cave, the player needs to defeat it in a Pokémon battle with a five minute time limit, to then have the opportunity to throw their Pokéballs at it.
Mewtwo in Generation Eight
Mewtwo is currently not available for capture in Pokémon Sword & Shield. Previously, from February 25 to March 2, 2020, there were special raid battles available for a limited time to celebrate the release of Mewtwo Strikes Back: Evolution on Netflix (how do they keep on missing Mewtwo's birthday?). However, this was only to try to battle an over-powered Mewtwo, not to catch it, similar to the final battle of Pokémon Stadium.
While there might be more special events in the future, in the meanwhile, the only way to obtain Mewtwo in these games is to transfer Mewtwo from another game through Pokémon Home. This can include permanently transferring the Mewtwo over from Let's Go Pikachu/Eevee. Or, if you pay for the premium version of Pokémon Home, you can do multi-console transfer gymnastics through Pokémon Bank to transfer Mewtwo from older games, including the Virtual Console releases of the Generation I games. It's still theoretically possible to do all the hops to transfer the Mewtwo up from FireRed & LeafGreen, although you'll need to pay Nintendo for the privilege, and the infographic is getting complicated.