Mewtwo

It inherited its DNA from Mew, and almost nothing else. The Pokédex entries say it themselves: the two have practically identical genetic codes, but their size and character are nothing alike. Here we have a two-metre, 122-kilo upright feline, with a thick tail and a tube coming out of the back of its skull and running down its back.

It doesn’t come from any animal or myth. It’s the product of a laboratory: a scientist spent years chaining together genetic-engineering experiments until he obtained it by recombining Mew. The Pokédex doesn’t soften the result—the man built the body and forgot to give it a compassionate heart, hence its reputation as the wildest of them all. Its official category, Genetic Pokémon, names a procedure before it names a creature.

It doesn’t evolve or descend from anything; the chain begins and ends with it. Its base happiness is 0, the lowest figure the game hands out, so it joins the team predisposed to like no one. What it does have are two Mega Evolutions that are nothing alike: Mega Mewtwo X, which becomes Psychic and Fighting with the ability Steadfast, and Mega Mewtwo Y, which remains pure Psychic and changes to Insomnia.

The 680 base points aren’t evenly distributed: 154 Special Attack and 130 Speed account for half of them, while the 110 physical Attack is leftover that almost nobody makes use of. Of its two abilities, Pressure costs the opponent two PP for every move it receives, something that only matters in long battles against other Legendary Pokémon, while Unnerve merely stops the opposing Pokémon from eating a Berry.

Psystrike, which it learns at level 72, is its signature move and the one that changes the calculations: it hits as a special move but calculates damage against the opponent’s physical Defense, so special walls that would survive a regular Psychic still go down. At level 40 it gets Aura Sphere, a Fighting-type move that can’t miss and puts the Dark and Steel types in its sights—precisely the ones that give it the most trouble. With Nasty Plot from a TM, two boosts leave that 154 in impossible territory.

The drawback is its own type. Pure Psychic has defended poorly ever since Dark and Steel existed: Bug, Ghost, and Dark hit it for double damage, and 90 Defense and 90 Special Defense don’t forgive a bad switch. A Kingambit that comes in with priority needs only one turn. The result is the usual one: it’s classified in Ubers and banned from standard play, alongside the rest of the restricted Legendary Pokémon.

Breeding is impossible. Its Egg Group is Undiscovered, it has no gender, and its Egg Move list is empty, so the 120 Egg Cycles listed in its data are an inert number—if they applied, they would amount to about 30 855 steps, one of the longest hatching times in the game.

What you get instead is a capture, and a difficult one. Its catch rate is 3, the bottom of the scale: at full HP and with an ordinary Poké Ball, the attempt is almost decorative, and the usual procedure is to bring it down to the minimum, put it to sleep or paralyze it, and accept that you’ll need plenty of Ultra Balls. It’s worth counting the turns, because Pressure drains the PP of whoever is holding out in battle.

Its habitat is listed as Rare, the label the first generation reserved for things that don’t appear on any route. In Red and Blue, it waits in the Cerulean Cave, opened only after the Elite Four, and it’s the only specimen in the entire game: once it’s gone, it’s gone. X and Y repeated the idea with another cave accessible after finishing the story, while Ultra Sun and Ultra Moon relocated it to Ultra Space, this time under Giovanni’s command.

It grows at a slow rate, gives 3 Special Attack EVs, and awards 306 base experience when it faints.