Kakuna

Ten kilos hanging from a branch. With 60 centimetres of yellow shell, this Pokémon weighs more than its hollow-looking outer casing suggests, and spends its life clinging to a tree without moving. Pokédex entries repeat it without embellishment: almost incapable of movement, it can only harden its shell to protect itself.

Inside, things are different. One entry explains that its body's activity runs at a frantic pace while it prepares to evolve, and that the proof is in the shell's temperature, hot to the touch. The stillness is only on the outside.

Its survival tactic is to hide among the branches and hold on until the change comes. If something corners it before then, it still has its stinger: it can poison an attacker without needing to move. It's the only offensive move it retains from its previous stage.

It occupies the middle step between Weedle and Beedrill, and is the briefest stage of the three: it appears at level 7 and disappears at level 10. Its official category, Cocoon Pokémon, describes exactly what it is — a pupa halfway through metamorphosis, with two curved protrusions in the centre of its body that foreshadow the stingers to come.

205 points spread across six slots, with the highest being 50 in Defense. Attack sits at 25, the lowest figure of any Poison type; Special Attack and Special Defense are also 25, and with 35 Speed it moves last against almost anything.

The spread is the least of its problems. The real issue is the movepool: in Brilliant Diamond and Shining Pearl, its level-up moveset runs out after one move, Harden, which raises Defense by one stage and deals no damage. It learns no TM, no tutor move and no Egg Move. A Kakuna sent into battle has no way to attack, and that's not a figure of speech.

Its ability, Shed Skin, cures status conditions at the end of the turn with a one-third chance. On another Pokémon it might make sense; here, it just makes the nothing last longer.

Bug and Poison resist Grass, Fighting, Poison, Bug and Fairy, which is a respectable list, but they open up four weaknesses: Fire, Flying, Psychic and Rock. All four are common on the routes you pass through with a Kakuna in your party.

Where it does fit is in a normal playthrough, and only as a formality. It yields 2 Defense EVs when it faints and gives 72 base experience, figures from an early-route Pokémon. The usual approach is to send it out for one turn, switch it out and wait three levels. In Red and Blue there was an amusing exception: Trainers who sent out a Kakuna had only Harden available, so the battle became a race between your damage and its Defense boosts.

Bug Egg Group, and that’s it. The gender ratio is 50% female, which avoids the bottleneck of male-skewed lines: any compatible partner from the group will do, and there’s no need to resort to Ditto to get started.

Its 15 Egg cycles work out to around 4080 steps, among the shortest stretches there are. That fits a species that only lasts for three levels. It has no Egg Moves, and in practice the question never even comes up: this form never hatches from an Egg, only Weedle does, so anything you want to pass on has to be decided with the final result in mind.

Its evolution requires nothing unusual. It evolves from Weedle upon reaching level 7 and becomes Beedrill upon reaching level 10. No items, no time of day, no friendship, no trading. With a Medium growth rate, those three levels take only a handful of battles.

Its habitat is the forest. Its catch rate, 120, sits in the middle of the table: neither the 255 of something that stays in the first Poké Ball nor the 45 of something that forces you to weaken and put it to sleep. It hardly matters, because almost nobody catches a Kakuna: it appears through evolution far more often than through a wild encounter.