I remember so many great times from playing. It was my first real adventure, and some of the Pokémon I met on that journey would become my favorites, such as Pachirisu. While I can't place any specific fond memories, I do have an even deeper craving to find a copy of the game I can restart. And with the anniversary here, perhaps I'll do just that.
As far as Platinum goes, my fondest memories always include the beginning of these games. I love going through every new save file and telling myself that I don't need Starly, only to end up with Starly in my time within ten minutes. The early Pokémon are very nostalgic for me (and I'm not easily nostalgic), and I love starting my new adventure every time.
My fondest moment would be when Dialga decided to alter history so that I never got to visit Sinnoh. Wait...
Probably getting a Leafeon for the first time and just wrecking everything with it that I could wreck with it
I played the games so long ago I don’t remember much... but for some reason I remember the most random events, such as -Cyrus’s Gyarados used Earthquake on my Empoleon and it fainted and I was confused how a flying type used a ground type move. -My Dialga had “Mischievous” as its characteristic and I didn’t know how to pronounce it -I brought a level 26 Bronzor with me into the E4. -I had a shiny Geodude named NachoCheez. [-My sister named all of her Pokémon based on their gender, even the genderless ones, like Bronzor was named Mr. Metal or something like that -I was trading with my sister and she gave me her level 45 Kadabra named Ava and then we learned that Pokémon could evolve by trade. -I played Diamond on this thing called TTDS and it worked similarly to an Action Replay. So when I learned how to use the cheats on the TTDS I made every wild encounter shiny, I made it so I could have 999 full restores, max number of all the TMs, etc. -I could also hack in the Manaphy egg, oak’s letter, key card thing, and the azure flute. That Arceus is in my brother’s Heart Gold. Man I was a dirty cheater/hacker.
The Sinnoh region was an amazing region but the fondest moment for me was actually getting lost in the turnback cave and going randomly through +50 rooms before getting to the exit. I think it took so long that I stopped playing and had to pick it up another time.
Giratina! Platinum remains one of my most favorite Main-Series Pokémon Game, and finally getting to Giratina and all that was a lot of fun.
using the e4 surf glitch to get to and capture Shaymin lol was only available in early Japanese copies of Diamond and Pearl (patched in all English versions iirc), which I am fortunate enough to own! capturing my first pokéradar shiny =) getting all the roamers oh my god what a pain but the satisfaction at the end was incredible!!
Catching my Spiritoimb that I would use doing the playthrough of Diamond, it was a hassle to get but worth it since I had a good defender with no weaknesses back then. Plus at that time it was something many didn't do or knew how to do so it made it feel extra special.