When Crown Tundra had released and I'd finished the grind for a shiny Regidrago (which I eventually found out in hindsight was full odds but didn't know at the time), my focus became on completing the crown tundra dex in a way that didn't involve tradebacks. This I knew was gonna suck for two reasons: Regieleki and Glastrier (I chose Spectrier, as did literally everyone else I knew so tradeback wasn't even an option). Bluntly I don't like how the DLC handled these at all, what with only being able to obtain one per save file, so it felt like it was gonna be hard to convince someone to let go of them, especially since they are strong pokemon (Glastrier mostly in trick room, admittedly). So my answer ends up being trading 2 shiny pokemon that I didn't care for and felt would be valuable to someone, using Home GTS.
The morning after I check Home. One of them gets me a Glastrier in a beast ball. Sketchy, but reasonable and cool. The other trade is this:
Understandably, I'm skeptical frame 1. For one thing, it's a shiny legendary traded on GTS. For another, in that moment I completely forget what I offered. I didn't talk about it publicly because I'm like "I just received a shiny legendary in GTS, this is not a legitimate pokemon", and I start doing hack checks, and I go "it looks fine, but I'm not like, gonna talk about it until I'm certain" and I forget about it for quite a long time.
Flash forward to very recently. Scarlet and Violet just came out and I'm starting to look into which shiny pokemon I'm willing to trade similarly for a Kubfu, which is something I could've done earlier but I didn't think to do it because the other Urshifu form isn't a new dex entry. I end up deciding I do want a rapid strike Urshifu, so I start looking, and I find the shiny Regieleki again in a box in Shield. So I do the usual hack checks, again forgetting what I'd traded for it, and find that:
- It has no ribbons - a weird one like the master ball tier ribbon would've been a dead giveaway.
- It has memories! (That thing you can do in pokemon centers in swsh - transferred pokemon have a "foggy memory" or something along those lines which is fine in that context, but is suspicious when it's a Pokemon with a galar mark.) Specifically it remembers being caught by someone called Phoenix (a different OT than the person who traded it to me: makes sense, since it's an english mon traded by someone with a Chinese name), which I'd guess is close to impossible to fake by hacking. Dunno how it'd work with cloning though. It also has a memory of me checking the town map and feeling lighthearted, which is meaningless in this context but cute.
- It only has 3 max IVs (The minimum number for a legendary caught from XY onwards!)
- It nature is Bold (-attack +defense) which is near useless for it and would need to be changed with a mint to be used in battles.
- It's at the level you catch it at in Crown Tundra, level 70, and has no EVs at all.
- The "first met" location is Split-Decision Ruins, which is correct.
- It's a star shiny, which is more likely than square for a soft reset shiny.
- It's in a level ball, which is sus, but if that was enough to completely write it off then the Glastrier I received wouldn't be legitimate either, but there are 0 reasons to doubt the legitimacy of the horse given that it's not shiny and also passes all of the above checks.
It also can't have any ability other than Transistor, and if it had its hidden even then on a legendary that's no longer suspicious as of Crown Tundra with ability patches existing. So logically it's... perfectly fine? But I still have my guard up, since it might be cloned which is something I know has had protections added for it lately as a countermeasure after The BDSP Disaster That Got Home Delayed For It, so I still don't mention it anywhere publicly.
And today I'm finally reminded of it again and decide to double check what I actually offered, cause that would be the final straw in deciding whether or not I lucked out and got a legitimate shiny, and in the trade history on Home it tells me it's the shiny Luxio. That's the first time I'd ever actually registered that this was a legitimate shiny for shiny trade, so I'm finally confident in saying it's legitimate and comfortable going "hell yeah, I have a shiny Regieleki!" All in all, the fact that someone chose to play nice and actually offer a legitimate shiny for a shiny on GTS honestly makes this one of my luckiest shinies and my reluctance to accept it also gives it a funny story of thinking for years it was probably cloned!
Oh, and as an afterthought, probably just gonna do a replay of Isle of Armor on a Shield save on another profile for the Kubfu after all, cause Plan A (trade a shiny) and Plan B (get a 2nd Enamorus and trade that for the like 500 people who are offering one for that on GTS) are both much less interesting than doing a 2nd save and playing the early game version of the DLC which I've never done before.