What are Pokemon that you DON'T want Ash to catch (or wish that he hadn't caught) ?

[Palamon]

None, really, but if I had to pick...Ash's Gible felt really last minute. I won't say I didn't want him to catch it, but I do honestly feel like this particular Pokemon should have been caught far earlier. But, I do wish he'd have caught Hipopatas instead.

& While this isn't a Pokemon that he "caught" I really wish he wouldn't have evolved his Snorunt into Glalie knowing Froslass was right there... I don't know, I just liked Ash's Snorunt as a Snorunt, never as a Glalie. Like, he barely used it as a Glalie anyway.

Also, Ash caught too many Pokemon in Unova. I wish he didn't catch Rogenrolla because he barely used it and it barely got any screentime.

 

[DuskAstral]

While it was neat to see how a Poke Ball worked should a Trainer have six Pokémon already,

This has already been shown twice.
In "Mystery at the Lighthouse", when Satoshi caught a Krabby, the pokéball was teleported to Professor Oak.

In BW018, when you caught your seventh Pokémon (this time it was Ash' Sewaddle), the Pokéball was sealed and could not be used until one of the other Pokémon was deposited.

 

[Alola]

This has already been shown twice.
In "Mystery at the Lighthouse", when Satoshi caught a Krabby, the pokéball was teleported to Professor Oak.

In BW018, when you caught your seventh Pokémon (this time it was Ash' Sewaddle), the Pokéball was sealed and could not be used until one of the other Pokémon was deposited.

And? If someone said they liked how Pikachu performed Thunderbolt in a specific way in a certain episode, would you come and say "We've seen it use Thunderbolt before."

I'm aware we've seen the phenomena before, but, as you pointed out, it had only been shown twice so far at that point. Across several hundred episodes. For the viewers who certainly have missed (or even forgot) either of the previous occurrences given that it rarely happens, they were able to see it in Palpitoad's episode, which was nice.

 

[Articfoxgamez]

This has already been shown twice.
In "Mystery at the Lighthouse", when Satoshi caught a Krabby, the pokéball was teleported to Professor Oak.

In BW018, when you caught your seventh Pokémon (this time it was Ash' Sewaddle), the Pokéball was sealed and could not be used until one of the other Pokémon was deposited.

Theres something a little messed up about a pokemon being stuck in a pokeball forever untill you go and deposit it or another pokemon.