Diglett

It nibbles on roots one meter underground and only comes to the surface after sunset. The Pokédex explains the schedule: its skin is so thin that, when exposed to light, its blood heats up and its growth is stunted. Living in the dark isn't a quirk; it's a necessity.

That diet has turned it into two opposite things, depending on who you ask. Several entries describe it as living farm equipment: wherever it digs, it leaves the soil tilled and fertilized, and some farms raise Diglett specifically for that reason, so the crops can be more productive. Another entry says exactly the opposite: it can cause havoc depending on the crop, because what it nibbles are the roots of whatever someone has just planted.

You can see the animal's head and nothing else. Twenty centimeters and 800 grams: the shortest and lightest Ground type in existence, with a pink nose taking up half its face. Its official category is Mole Pokémon.

At level 26, it evolves into Dugtrio, which is three of these poking out of the same hole. In Alola, the species developed three golden whiskers from living in iron-rich soil; they work as sensors and also as a mood thermometer, standing stiff when it gets angry and drooping when it's sad.

A base stat total of 265 is one of the poorest spreads in the Pokédex, and almost all of it goes in one place: 95 Speed. The rest is 55 Attack, 45 Special Defense, 35 Special Attack, 25 Defense, and 10 HP. That last figure leaves no room for nuance — any neutral hit knocks it out, and several priority attacks do too.

What keeps it going isn't any of those numbers, but Arena Trap, which prevents the opponent from fleeing or switching out. With that, a 10-HP bug becomes a hitman for hire: it comes in after one of its own has gone down, traps a weakened Steel or Rock type, and finishes it with Earthquake, which it learns at level 40. Stone Edge, learned via TM, covers Flying and Fire types. Swords Dance, also via TM, turns that 55 Attack into something that genuinely kills, and Sucker Punch, at level 20, moves first whenever the opponent attacks. At 44, it gets Fissure, which never misses when it hits and almost never hits.

The problem was never Diglett, but its ability. Smogon banned Arena Trap from seventh-generation OU after a suspect test, arguing that it barely allows any counterplay, and the species has gone through several of its own suspect tests in Little Cup over the years. Trapping also doesn't work against Flying types or anything with Levitate.

In a normal playthrough, its role is different and comes early: Dig at level 32, backed by 95 Speed, handles Electric, Rock, and Poison Gyms before anything can hit back.

It belongs to a single Egg Group, Field, the busiest of them all, so it can breed with almost any land animal on the list. The gender ratio is fifty-fifty. Twenty incubation cycles are about 5355 steps, one of the shortest times around.

Five moves come from the egg: Headbutt, Ancient Power, Memento, Hone Claws, and Endeavor. The last two pull in opposite directions. Hone Claws raises Attack and accuracy, exactly what a physical attacker with accuracy issues wants; Endeavor deals damage equal to the user's remaining HP, and with 10 base HP that's a laughable figure. Memento, on the other hand, makes good use of what it has: it faints to leave the opponent with both attacking stats at rock bottom.

It evolves into Dugtrio upon reaching level 26, with no items or additional conditions. It grows at a medium pace, so it reaches that level without falling behind or pulling ahead of the rest of the team.

Its habitat is caves, and its capture rate, 255, is the maximum possible: an ordinary Poké Ball will usually do the job without weakening it. It sometimes holds Soft Sand. Defeating it gives 1 Speed EV and only 53 base experience points.