Raichu

It closes out a three-stage line that starts with Pichu and goes through Pikachu, and it's the only step that isn't gained through levels or affection: you need a Thunder Stone. The animal underneath is still the same mouse, only now with orange fur instead of yellow, long ears and a thin black tail tipped with a lightning bolt. Beneath that lies something older than the rodent: the raijū, the thunder beast from Japanese folklore, described as a small creature resembling a weasel or squirrel that fell with the lightning.

Pokédex entries keep insisting on one particularly unpleasant detail. When charged with electricity, its muscles tense up and it becomes aggressive, to the point of attacking its own Trainer if they let their guard down. When the cheek pouches build up too much charge, it plants its tail in the ground to discharge it, which is why scorched patches are often found around its burrow. At rest, it emits a weak current that makes it glow in the dark. The 100,000-volt discharges mentioned in the text are powerful enough to knock down Pokémon much larger than it.

Eighty centimetres and 30 kilograms, Mouse Pokémon category, forest habitat.

The spread of its 485 points makes its purpose obvious: 110 Speed ahead of everything else, 90 Attack and 90 Special Attack, followed by the disaster — 60 HP and 55 Defense. One neutral physical hit is enough to leave it hurting, and any priority move finishes it off. It either beats the opposing team through sheer speed or it doesn't beat it.

Being pure Electric has the advantage of a single weakness, Ground, along with resistances to Flying, Steel and Electric, and an immunity to paralysis. Offensively, the type hits Water and Flying hard and runs into Grass, Dragon and Electric itself; it does absolutely nothing against Ground, so coverage is not optional. Thunderbolt, which it learns at level 5, is the go-to attack; Volt Switch lets it hit and get out before eating the response; Focus Blast and Dig patch up the holes. Nasty Plot is the only way it has to turn 90 Special Attack into a number worth fearing.

Lightning Rod, its Hidden Ability, is the most interesting thing it brings: it absorbs Electric-type moves aimed at it, nullifies them and raises its Special Attack. In Double Battles, that turns Raichu into a shield for the partner that actually fears Electric. Static, its regular Ability, paralyzes on contact and not much else.

The underlying problem isn't Raichu's: Light Ball doubles both of Pikachu's attacking stats and doesn't work on the evolved form, so the Thunder Stone becomes a losing trade as soon as that item enters the picture. Outside of that, it does more than enough in a normal playthrough: it gets there quickly and hits from both sides. There is no plan against Ground types, and Dugtrio also cuts off its escape.

It belongs to the Field and Fairy Egg Groups, with an even 50% gender split, so any specimen will do for breeding without having to pray for a female. Its 10 Egg cycles work out at around 2805 steps, among the fastest there are. Pichu hatches from the Eggs, never Pikachu or the final form. It has no unique Egg Moves: everything it learns comes through levelling, TMs or inheritance from the baby stage.

Its evolution condition is a single one with no room for interpretation: expose Pikachu to a Thunder Stone, with no minimum level, no friendship and no time-of-day requirement. It's irreversible. The practical consequence is that its level-up movepool runs out almost immediately — Thunder Punch at 0, a huge block at 1 with Thunder, Thunder Wave, Iron Tail, Agility, Nasty Plot and Electro Ball among others, and Thunderbolt at 5. After that, nothing.

In the wild, it appears in forests and sometimes carries an Oran Berry. Its catch rate, 75, puts it in no man's land: it's not the walkover that a common Pokémon is, but it's not the 45 of species that force you to empty your bag of Ultra Balls either. It grows at an average rate and yields 3 Speed effort points, which fits the one thing it does well.