Celebi

Its head is a still-closed lily bud, with two blue-tipped antennae and large eyes outlined in black. It has a pair of transparent wings on its back, three fingers on each hand, and oval feet with no toes at all. Sixty centimetres and five kilograms: it fits in the crook of one arm.

What it does is not nearly as small. The Pokédex entries all insist on the same thing — it travels through time, and came from the future by making that journey. Grass and trees grow across the fields it passes through, and besides revitalising vegetation, it can also heal wounds. Its status as the guardian of the forest has been confirmed in documents preserved from different eras, which is a careful way of saying that people have been watching it appear and disappear for centuries. It only shows itself in times of peace. As long as it keeps appearing, the belief recorded in the Pokédex says, the future remains hopeful.

Its official category, the Time Travel Pokémon, describes exactly what it does, which is unusual in a Pokédex full of vague labels. It does not evolve, it does not come from anything, and it has no alternate forms: number 251 closes the Johto Pokédex all by itself.

One hundred HP, one hundred Attack, one hundred Defense, one hundred Sp. Atk, one hundred Sp. Def and one hundred Speed. Six hundred points without a single peak, which means it takes hits, hits back and runs above average across the board, but never beats a specialist at anything. That 100 Speed is an old and respectable benchmark, not the kind of number you see on a modern sweeper.

Natural Cure clears its status problems as soon as it returns to its Poké Ball, so any poison or burn thrown at it lasts only until it switches out. In the wild, it holds a Lum Berry, and the combination of the two explains why it is so difficult to shut down with status.

Offensively, its two types are nothing special: Psychic and Grass run into too many resistances. Giga Drain restores half the damage dealt, Energy Ball hits for 90 with no secondary effects, and Leaf Storm, which it learns at level 90, fires off 130 power at the cost of leaving its Sp. Atk in the gutter. Calm Mind and Nasty Plot let it set up from the back.

What holds it back is its defensive typing. Grass and Psychic add up to seven weaknesses, and the Bug weakness is fourfold: any old U-turn, a move half the format carries as standard, takes it straight out. The physical route is no better: it learns Swords Dance by TM, but its best physical moves are Facade with 70 and Aerial Ace with 60, neither matching its types. And its status as a Mythical Pokémon keeps it out of official formats, which usually exclude Mythicals.

It cannot breed. It belongs to the Undiscovered Egg Group, has no gender, and there is no way to produce one of its Eggs: the 120 incubation cycles listed in its data, about 30,855 steps if the formula were applied, are a figure that never gets used.

It is obtained in other ways. The original method is in Pokémon Crystal: with the GS Ball in your Bag, the shrine in Ilex Forest made it appear, an event that at the time was only available in Japan and that the Virtual Console re-release eventually opened up to the rest of the world. Outside that, it has all been distributions — the Japanese World Hobby Fair in 2001, that year's European Celebi Tour, the anniversary distributions in 2006 and 2016 — and transfers from earlier generations through Pokémon HOME.

Its catch rate, 45, is an interesting detail: it is the same as a starter Pokémon's, not the 3 that almost all Legendaries have to fall back on. Anyone who gets it in front of them can catch it without much trouble; the hard part is getting there. It gives 3 HP EVs when defeated, has 100 base friendship and grows at a Medium Slow rate. Its recorded habitat is the forest, and in the wild it holds a Lum Berry.