Okay so I have no explanation for this and I know this will sound very unbelievable, but bear with me. I will give as much disclosure and information as I can, so that perhaps we may figure out if this is something legitimate or not.
I have spent the past few hours resetting my clock to 11:58PM over and over to farm Stadium 2 Mystery Gift (trying to get Scope Lens and Mysteryberry "legitimately")
On this Gold save file, TID 28821, I only just reached Goldenrod about a week ago to unlock Mystery Gift. My most recent save backup was in Azalea Town on December 19th, and the only decorations I have according to that backup are Deco Plant 4 (not sure what this is), Deco Bed 1 (default I'm sure), and Players Room Poster (Town Map poster I think). I backed up this save because originally, I had the TID set to 00007 from the start of the game (not sure what TID the game actually gave me). I switched the TID at this point, before reaching Goldenrod and ever using Mystery Gift, because I wanted the set of Mystery Gifts that would come with TID 28821
I am positive that I have not backed up this save since then or modified it since
I was in the midst of resetting the clock for Mystery Gift over and over and was getting fed up with not getting the items I need, so I took a break and decided to decorate my room in Stadium 2
To my utter disbelief, a Surfing Pikachu Doll and UNOWN DOLL are sitting in my inventory
Along with Clefairy, Squirtle, Diglett, Staryu, Magikarp, Gengar, Shellder, Voltorb, Weedle, Geodude, and Machop Dolls
I also have Red, Blue, and Yellow Carpets
TropicPlant and Jigglypuff Poster as well
Everything in bold is decorations that TID 28821 cannot receive through Stadium 2 (some of them can't even be received by TID 00007 either)
I have not Mystery Gifted with any cartridge saves, as I only have one Game Boy Color at the moment
Unfortunately, I did not record the majority of this process. I only recorded about 12 minutes of myself resetting, before changing my mind and ending the recording because I felt like it would take far too long to get what I wanted. For context, I've been Mystery Gifting Carrie for about 3 hours or so. The idea was just to record myself getting Mysteryberry and Scope Lens for proof if my stream chat asked how I acquired them and if I cheated them. I did record myself getting a Mystery Gift on stream last night https://www.twitch.tv/elsteeler/clip/ExuberantVastLapwingVoteYea-9-4pSB6zGSBgjoUR
And ironically, I stumbled upon something much, much more suspicious
My theory is that somehow, letting the clock roll over and farming Mystery Gift like this has screwed with something in the Mystery Gift. Maybe a flag isn't getting reset or something, I don't know. But I believe that I am somehow also receiving the decorations that Carrie received. I say this because in the Twitch clip, Carrie says she got an Unown Doll. I didn't register this at the time, but she also said this before I even Mystery Gifted her. I'm not sure if she usually says something but the dialogue makes it clear that I am meeting her for the first time, immediately followed by her Unown Doll dialogue. She's also been making comments about receiving other decorations. I for sure remember her getting multiple Carpets, while I have "received" none from her. Yet they are in my inventory.
As far as the decorations that I actually remember receiving, it's Squirtle, Gengar, Voltorb, Weedle, TropicPlant, and Jigglypuff Poster. And those are all possible for my TID thru Stadium 2 anyway. I definitely do not remember receiving any of the gifts in bold, nor anything else I didn't mention.
My process, for anyone who wants to try this:
1. After taking that day's Mystery Gift, go into Game Boy Tower and reset the clock to the next day at 11:58pm
2. Save the game in a Pokemon Center
3. Exit Game Boy Tower and Mystery Gift with Carrie. If she sent an item, enter the Lab and receive the gift from Oak.
4. Wait until clock runs over to 12:00am the next day, and Mystery Gift with Carrie again. If she sent an item, reenter Lab and receive second gift.
5. Repeat step 1 and so on
During this process, I have definitely gone too fast and tried to Mystery Gift before the clock rolled over to 12:00am, several times. I'm not sure if that also has something to do with what's happening. Just in case it becomes relevant, I also should mention that I have Crystal in my port 1 Transfer Pak and Gold in my port 2 Transfer Pak. I Mystery Gifted Crystal only twice, for yesterday 1/1/25 and today 1/2/25 since I have not messed with that in-game clock. That Crystal save is TID 00007 and does not have any unexpected decorations.
I plan to recreate this situation at some point with a different, fresh save that has just reached Goldenrod and never been modified. I'll record the entire process and check the room frequently for new decorations that haven't been properly received. If anyone out there is interested or curious, please let me know if you find anything.