Pokémon
Pokémon was a special interest for me from about 5 yrs to 12. I was very attatched to it, for a long, long time. It eventually faded out, probably because the games were getting considerably more expensive. It also could have just been a natural shift to other likes. Despite this, I still ADORE Pokémon. I play it considerably less often now but it's still a nice timekiller.
I had been working on a living dex for years, but I've pretty much stopped with my loss of interest. I had almost all of them, only missing about 10-20 'mons. That was before Scarlet and Violet came out, anyway. I'm a far more casual player, picking random Pokémon and giving them pretty movesets and just bonding with them. I HAVE tried competitive, but I suck at it. I would not have lasted another day overanalyzing stats and movesets.
Favorites
I have plenty of favorite 'mons. My absolute favorite is definetly Archeops, and my main partner for self inserts and my Pokémon Sword file is an Archeops named Calypso. Here's some art I made of him!
Otherwise, I really like Bug types and Steel types. Some specific favorites are Butterfree, Silvally, Charcadet and its two evolutions, Scyther, Xurkitree, Mismagius, Hisuian Zorua, and Skarmory, among others. I'm more inclined to use Pokémon that I like during a playthrough rather than anything related to stats, as long as I can eventually beat the game with them.
I think of my "home region" as Hisui, specifically the Alabaster Icelands. I would 100% be a Pearl Clan member as well. In that specific setting, my partner is a Hisuian Zoroark named Vince. I also like Alola a lot, mainly because I had played Ultra Sun a lot during the peak of my Pokémon hyperfixation. My favorite Pokémon game is PMD: EOD. I do like all PMD games, however! :-D
Collection
I have a LOT of Pokémon related stuff, it was pretty much the only thing that I ever got in gifts for years. I've been thinking about getting rid of a punch of it to make room, but it's difficult... a lot of it still holds a lot of sentimental value. I have a couple of books, posters, toys, plushies, figures, and even a Greninja amiibo.
My largest collection is my Pokémon cards. I could probably sell them for a lot, but I can't find it in my heart to :-(. I have several rare ones, like a Base Set Blastoise (unfortunately neither Shadowless or First Edition). My favorite card is a Jungle Butterfree that's hung up, safely inside a card sleeve that's taped to my wall. I also have a Latias Gold Star that I could sell for a pretty penny if it wasn't as beat up as it was. I think its real pretty, though. I scammed a friend out of it in 4th grade.