Just Pokedex Filler

What Pokemon in the Pokemon games do you feel are just "Pokedex filler"/Pokemon you think were created just to fill space and feel less necessary than the others?

For me, Basculin in the Unova dex (before it got an evolution in PLA) and Volbeat and Illumise. For Basculin specifically, it's a one stage evolution fish that genuinely feels like it existed purely to fill a space in the Pokedex.

Volbeat and Illumise feel as though they were solely created to show off the double battle mechanic, and nothing else. I feel like Plusle and minun fulfill this role better than Volbeat and Illumise, though, so for me they just "fill up Pokedex space" since no one even really uses them in the Hoenn games, to begin with. They're also only in one place on the Hoenn map, I believe and you can easily miss them. So, seeing one just "fills out my Pokedex".

Almost all the Pokemon in the generation I games that are trade only. But only in generation i. Never felt they were necessary, but you have to get them in gen I to complete your Pokedex. But, I just feel like they're a spot to fill in and don't care.

Other than that, I can't think of any others I deem as "pokedex filler" and "just another slot".

- Unown. Knows one move. Could have used a normal alphabet.

- Azurill. Serves no purpose. Gives other awful baby Pokemon like Igglybuff a begrudging (and probably too generous) pass. Introduced breeding mechanics with those babies. Stuck Azurill in in Generation 3. Eliminates that excuse.

Considers Marill quite weak already (250 base stat points, 1 less than Pidgey). What is the point of adding in a 190 base stat Pokemon?

- Volbeat and Illumise: Agrees. Gave Minun and Plusle doubles-based abilities. What did Illumise and Volbeat get? Helping Hand at level 33? Weak.

- Wynaut: See Azurill.

- Luvdisc: What has this fish ever done? Exists to hold Heart Scales.

- Basculin: Ditto on that. Tread on the same ground as Carvanha and Sharpedo.

- Tynamo or Eelektrik (probably the latter): Gave Tynamo nothing to work with. Notices very minor changes between Eelektrik and Eelektross. Could have deleted something in this line.

Edit:
- Pachirisu: Just Sinnoh Pikachu.

- Silcoon or Cascoon. Why split this line here? Never notices the difference without paying close attention.

Mantyke doesn't feel necessary in the slightest.

The leaked Pokémon Gold Spaceworld ROM showed a lot of baby-Pokémon concepts (baby Growlithe, baby Vulpix, baby Tangela, baby Ponyta), and it's great that they never came to fruition, frankly.

Separate to that point: there have always been Pokémon without evolutions. Lapras, Aerodactyl, Girafarig, Stantler. Some of these are great, very usable in-battle, with cool designs.

Then there's Carnivine, Kecleon, Spinda, Maractus, Stunfisk.. to name a few. Visually they're reasonably unique, but we virtually never see them used by any trainers of significance. Carnivine is an especially sore spot, because of how difficult it is to catch.

Mr. Mime, Golem, Pinsir, Porygon in Gen I since they more or less gated behind some easy to miss mechanic or were just very annoying to get.

Mew and most mythicals really - they're made to be impossible to get and event bait. Even if you don't need them to fill your Pokedex it fulfills the same basic purpose of being extra stuff to catch that's gated behind some other game mechanic (in this case, glitches or events).

Smeargle, Natu / Xatu, Misdreavus are also located only in one place in Gen 2 and are easy to miss - in Misdreavus' case, on the last area of the game even.

Besides the Pokemon that were already mentioned here, Beldum is arguably a Pokedex filler in Gen III and is just there to fill the "pseudolegend" requirement since you can't even get it until beating the post game, the first stage can only use one move and is a pain to train up all the way to Metang / Metagross.

Nebby is somewhat justifiable due to story reasons - they needed an excuse for the plot to not have Solgaleo / Lunala from the get go - but its middle evolution is not and is just a waste of time for everybody involved (even if I do like the design).

Which brings me to my point, new games have new Pokemon and move availability and that makes Pokemon better or worse and so the title of "Pokedex Filler" is kinda time dependent.

Porygon was kinda crappy and obscure in Gen I, but after Gen II and III it became recognized as an important staple of competitive due to Porygon-Z / Eviolite Porygon2. Smeargle was always useful in Competitive due to its gimmicky nature ... until they banned Spore / nerfed Dark Void and banned Baton Pass, then its usage in the standard tiers dropped like a rock (although I'm sure it's gimmicking up in AG somewhere). Misdreavus was more or less an obscure trivia (not even the Ghost gym leader in the generation that introduced it used it!) until Mismagius came along.

Mawile was forgettable as heck until Mega Mawile and Fairy typing dropped making it a power house. Sableye went from curiosity with no weaknesses, to master troll with Prankster / Mega Sableye + Magic Bounce.

-Pichu, Cleffa, Igglybuff, Azurill. Pointless baby forms for already weak Pokémon that in some regions you can catch before the first or second gym.
-The whole Wurmple line. Very uninspired Caterpie/Weedle replacement.
-Corphish/Crawdaunt
-Plusle, Minun, Pachirisu, Emolga, Dedenne, Togedemaru, Morpeko: All created just to cash in on the Pikachu fan-service even more.
-The elemental monkey trio. Very uninspired filler.
-Munna, Roggenrola, Timburr, Woobat, Bouffalant, too obvious replacements of their Kanto counterparts.
-Basculin
-Alomomola
-Klang and Vanillish specifically: This lines clearly aren't inspired enough to justify three stages, the middle stages seem like Pokédex fillers.
-Perrserker: I hope having a new regional Meowth in every gen doesn't become a new tradition.
-Cresselia, Shaymin, Keldeo, Diancie, Zeraora, Magearna... and any other legendaries/singular Pokémon that have no plot whatsoever and are basically just created for special events, encouraging pre-orders, and make people watch Pokémon movies.

Most of the ones that came to mind are already mentioned, but I'll add in Poliwrath/Poliwhirl.
They are basically the same mon imo, one is just angrier. The differences are so small.
Could've easily either skipped the middle stage or make Poliwhirl a Water/Fighting type and make it the final evo.

Before I read any of the responses, Basculin. Ok, it seems like we're on the same page with Basculin. And I'll also agree, a lot of gen 5 mons are filler. Sigilyph, Cryogonal, Woobat line, Munna line, and Yamask line, to name a few. Also mons like the Burmy line, Nickit line, Bruxish, baby Pokemon, ...

While I think it is adorable, Phione. I still really don't think it's necessary with how massively similar it looks to Manaphy and still wonder why it's around.

Oh, and while I love Maractus, I feel like with Cacnea and Cacturne it wasn't too necessary and just exists to fill a specific slot in Unova. :(

Also Bruxish!!

Did anyone mention Basculin? Okay good.

So many unneeded Water types and Pikachu clones.

oof, maractus. it's a nice design, but I forget it exists since the cacturne line is there. carnivine too. cool to have a venus flytrap, but bellsprout is already there.