Pokémon you used to dislike, but like now

[Kater Karlo]

From a story/normal gameplay standpoint, I've never liked Lucarios' moveset. The fact that it doesn't get bullet punch, a completely fitting steel move, and really doesn't get any steel moves besides flash cannon without a move tutor/TM has always made it a really underwhelming choice, especially since getting one is a friendship evolution. It felt especially redundant in Gen 6 and later, when there were so many other good fighting or steel options. I like the concept of Lucario, but I feel like as time passed, it became clear how little it contributed other than a cool mascot image.

 

[Claymore of Ashes]

For me it was the Normal type itself. When I was younger, I thought it was useless. But now I see it's utility as being almost unmatched, especially as setup mons.

 

[Squirtkipfan01]

Honestly bugs and grass in general, but ive found some i like over the years(the scyther lineup and breloom to name 2)

 

[Corveone]

Although I never disliked them, there are some Pokémon that I used to ignore when they first came out, and had no interest in adding to my team. But I ended up giving them a try for different reasons, and they actually did great and were much better than I expected.

Azumarill, Masquerain, Bibarel, Lickilicky, Gigalith, Cinccino, Trevenant, Ribombee, Comfey.

The opposite happen with certain other Pokémon, which I had much higher expectations in and ended up being rather meh.

 

[TwilightBlade]

I like a lot of Pokemon from the start, but here are some I didn't grow fond of until after they were introduced:

Hippowdon/Mamoswine - I always thought they were kinda boring with their brown color scheme, but I started using them in BDSP/Pokémon Go. They're quite bulky and strong.

Ambipom - its tail freaked me out for about a decade. It grew on me during my BDSP playthrough. It's fast and strong with Technician as well.

Decidueye - PLA made me like it a lot more than its debut in Sun/Moon. It has a lot of personality with the archer motif.

 

[KalloFox34]

I've always liked them, but Sandslash, Absol, and Delphox are Pokémon that I've really begun to appreciate a lot more recently.

As for Pokémon that I outright disliked, I used to think Cramorant looked really stupid. After giving it a chance in one playthrough, I found that it was really fun to use due to its ability. It was also surprisingly strong and I could always count on it on the (admittedly rare) occasion that I was in trouble. The ugly-cute design also kind of grew on me.