Which Pokémon do you always catch but never use? For me it's the Unown. They are too weak with only 1 attack.
Personally, I never catch a Pokémon I don't plan on using, but I think (if only fully-evolved Pokémon are considered) that the Pokémon Sudowoodo, Wobbuffet, Girafarig, Dunsparce, Corsola, Delibird, Mantine, and Stantler are some of the most unused Pokémon in the introduced in Generation II. None of them are really amazing at battling, but that's not to say they don't have their fans!
Sudowoodo and Girafarig kinda don't have a lot going for them in battling due to being outclassed by other Pokémon that can do the same thing (A shame, because I actually really like Girafarig's design, and was hoping it'd get a mega where the tail head goes crazy evil). I've actually seen a huge Dunsparce following, and it can actually be pretty fun to use in battle with that Serene Grace headbutt! XD And then there's Unown. You simply just can't battle with Unown
Pretty much any dragon-type pseudo-legendary. They evolve at such high levels and I am really impatient when it comes to EXP farming. Even though they are really strong, I never use them for that one reason.
I have to say, I've never seen anyone willingly use a Furret or Farfetch'd, not even in regular playthroughs.
I've use both. I love Furret, and used one in my most recent Gold playthrough. Farfetch'd is pretty good for the gen 1 games since you can get one pretty early through trade. It's pretty strong, learns fly and cut, and levels up faster since it's a traded Pokémon. As for a Pokémon I never use, probably Noctowl and Togetic? I love them so much, but they just don't hold up very well in gen 2. Does anyone use Qwilfish? Genuinely curious, because a lot of the time I forget it exists.
I like using Noctowl, but I don't remember using Furret much outside of being an HM-slave. Qwilfish is just kind of odd, since it doesn't evolve and is generally inferior to Tentacruel as a Water/Poison Pokémon; the only reason to use it is as a Spikes/Toxic Spikes spreader...
I would say the some of the single stage Pokémon that were introduced in the gen, with the obvious exceptions of course. (Skarmory, Smeargle, Heracross, etc.) I've never seen people use Delibird and Quilfish.
I use Furret, I'm actually using one right now. It gotta be Unown for me, I actually like the mon and that it can be a whole alphabet but with it only ever learning Hidden Power is not worth using sadly.
I'd probably say Delibird is one of the least used. It has poor stats 45/45/45 for hp and defenses, 55/65 for attacks, and its highest being 75 in speed... which is still nowhere near fast. Its typing Ice/Flying is one of the worst defensively (super effective x4 from rock, x2 from steel/fire/electric and resists only 2 types grass/bug with one immunity to ground). On top of all of that, in gen 2 the only level up move it gets is Present! If you want your Delibird to know other moves you'll have to resort to TMs. Here is the thing about Present though. It's completely luck based, and can sometimes HEAL YOUR ENEMY. Delibird's attacking stats are so low anyways that if you are lucky enough to get a strong attack chance, it still wont do much. Present isn't boosted by Delibird's Stab either which makes it even worse. While Delibird may be cute and a festive Christmas Pokémon... I never use it because it is just so frustrating to train and battle with.
Well, the only Pokémon I ever catch that I don't plan to use are legendaries. (So yeah, as much as I love Lugia, I haven't used him since I caught him) By the time I capture one, I always have my main team of six, so by that point, I have no reason to use the legendary. I only catch them because I feel like I have to. Other Pokémon I don't use are the ones the game hands over to me, like the dinosaur of my choice in gen 6, all those free Pokémon in Omega Ruby and so on. In the case of Johto, it's Togepi.
It seems quite a few gen 2 Pokémon went unused by people in Gold/Silver due to being so rare and hard to get and how there are better options in Pokémon from gen 1. Why bother using Quilfish when Tentacruel is better and more common for example?
Honestly, Larvitar. I fucking love that Pokémon, but it comes on the last god damn location of the game where you don't have ANYTHING to do. I was so damn eager to have one in my team back then that when I caught him I grinded up Red and the e4 so much to the point they developed a BDSM fetish just so I could have it in lvl 100. Did the same thing with Dragonite because I couldn't find dratini but on that game it was kind of my own fault. No I didn't know about the game corner, but also... screw that, I hated that thing besides the music.
Unown 1 move with a unknown typing (some NPC tells you what typing it really is for the Pokémon) that does little damage at 20 PP.. You can't even use Unown in Contests or Pokeathalon for the most part...