In this thread, we sometimes have to stretch the definition of "Worst" a little bit. There are many ways to define a bad Pokémon, and if we were to all take the thread title literally, the thread wouldn't have more than two pages' worth of everybody agreeing that the answer to its question is Simisear. Indeed, to allow for a varied and fruitful discussion, we sometimes have to look beyond that turd of a monkey and seek out some Pokémon that are bad in certain categories or aspects. Whether it's bad usefulness, uninspired visual design, boring gameplay design, uninspired lore, or other things that make certain Pokémon worse than they have to be.
Besides, I wanted to talk about this and this was the only thread I felt it could be sort-of relevant if I wrote a paragraph justifying it first.
In the category of "Pokémon Game Freak designed and then clearly forgot about", enter Bergmite:
To be honest, I don't see much wrong with Bergmite's design. It's the Ice Chunk Pokémon, and wow does it look like a chunk of ice. It has a recognisable silhouette, some decent (if generic) lore, and a movepool as passable as it gets for physically-based Ice-type Pokémon (that is, as barren as the Antarctic interior, but Bergmite doesn't stick out in this respect).
However, Bergmite is, how do I put it,
obscure. It has been four years, and nearly four pairs of core series games, since Bergmite debuted in Pokémon X and Y. However, X and Y remain the only games it is available in (not sure about USUM, but I'm not holding my hopes up). It is also found in Pokémon Shuffle (as are all other Pokémon, to my knowledge), Pokémon Rumble World (what is even that?), and Pokémon Battle Trozei (No, I hadn't heard about it before either, and even Bulbapedia doesn't have more pictures of it than the logo). In short, Bergmite is only available in one game people are likely to play. It also has only one appearance in the Anime, where it wasn't even the Pokémon of the Day.
But so what? It probably shares this distinction with plenty of other Pokémon. Okay, it is only found on two floors in one dungeon of the game, but it's not an optional one, and you're likely to bump into at least one thanks to its 20 % encounter rate. Doesn't hold a candle to, say, Chimecho in RSE. There's nothing to stop you from popping one on your in-game team and playing around with it for a while?
Here's the thing, though: Bergmite evolves at level 37, into the considerably more distinctive and memorable Avalugg. However, Bergmite is only found at levels 39 and 40. This means that
Bergmite is not encounterable at a level below that which it evolves at. It's overdue for evolution already by the time you catch it. Avalugg takes over the spotlight once Bergmite is raised a single level, unless you force it not to evolve. It takes some considerable backtracking and breeding for you to obtain a Bergmite you can level up without either evolving it immediately or holding off evolution, and by the time you baby the newbred Bergmite to a level where it can pull its weight for that point of the game, it's ready to evolve anyway.
Basically, Bergmite is outdated from the moment you find it, and to rub salt in the wound,
it's the only moment you find it.
I don't know what the designers were thinking, to be honest. Was Bergmite intended to be found at an earlier point in the game, was the level curve tweaked so that Frost Cavern's general level level was above Bergmite's evolution level, or were they completely aware of this but decided to leave Bergmite evolving at 37 so it could be featured earlier in some future game? After all, they've kind of painted Rufflet, Vullaby, Pawniard, and others pretty solidly into the late-game corner for the foreseeable future. There's nothing preventing those from being used in the early-game, but they are rather un-fun to use since they evolve after level 50, meaning you will have to drag a first-stage Pokémon around for most of the game. Did the designers want to save Bergmite from that fate? Or was it simply a big oversight?
I believe Bergmite is the only Pokémon with this unique distinction of not being available in-game below its evolutionary level, but if you can think of any others, please tell me!