Are there any Pokémon that get weaker when they evolve?

Question

Just popped into my brain

This can mean in terms of BST, but also factors that make Pokemon less usable such as a worse typing, ability or other factor that hinders the Pokemon when compared to its previous form.

Comments

What do you mean by weaker? Smaller Atk or Sp Atk stat? or is the non evolved form better competitively?

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Safe to say no Pokemon has a higher BST than its evolution. However in some instances it could be possible that a Pokemon can be more viable in competitive than it evolution, due to typing or ability etc.

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I think this has been asked already: https://pokemondb.net/pokebase/218503/what-are-all-pokemon-that-decrease-stats-while-evolving and https://pokemondb.net/pokebase/311749/which-gen-7-pokemon-lose-stats-upon-regular-evolution

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Terlor, AHEM, Shedinja.

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I decided to edit this one a bit. I think we can make it a bit broader than BST, as was the focus of the two other threads -- the answer below already does this. Let me know this isn't okay. Thanks for flagging.

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Oh, Okay.

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By weaker I mean some stats drop

Answer 1

Technically, Shedinja has a lower stat total than Nincada, but I think it's still useful. Scizor isn't necessarily weaker than Scyther, but it has the same base stat total, making Scyther a popular not-fully-evolved Pokemon. Other Pokémon like Slaking, Chansey, Type: Null, and many more can be argued to be worse than their pre-evolutions, but not in base stat total. This makes Shedinja the one-and-only special Pokémon to be "worse" than its evolution in stats.
Source: Pokemon DB

Comments

There is also Chansey, which is distinctly better than Blissey due to Eviolite as per your other examples.

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(Cross Choping Machamps will always kill Chansey. Oof.)

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I hate chansey

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Who gave you the idea that Raichu's worse than its pre-evolution? It's used on almost 90% of electric Monotype teams.

Answer 2

These Pokemon have at least one stat that's lower than its pre-evolution's stat.

metapod, metapod, butterfree, kakuna, kakuna, beedrill, poliwrath, politoed, magnezone, steelix, tangrowth, scizor, electivire, magmortar, porygonz, porygonz, honchkrow, octillery, silcoon, silcoon, silcoon, beautifly, cascoon, cascoon, cascoon, nuzleaf, pelipper, ninjask, shedinja, shedinja, vibrava, armaldo, salamence, vespiquen, leavanny, whirlipede, scolipede, scolipede, crustle, escavalier, eelektrik, accelgor, accelgor, volcarona, spewpa, spewpa, vivillon, aegislash, incineroar, toucannon, charjabug, vikavolt, vikavolt, crabominable, toxapex, mudsdale, golisopod, solgaleo, solgaleo, lunala, lunala

source: a modified version of this thing