Pichu is adorable, and I had an idea. If somebody were to catch a small Pichu worthy of the Teensy Mark, transfer it to Sword (or any game that has Marks), play with it and battle with it, transfer it back to the original games (Scarlet/Violet), would the Mark still be there? And does the Mark appear in-game when you check the summary of the Pichu in Sword or Shield?
At this point, ya know the drill. Hide if it's a dupe. And this isn't just for Pichu. It's for any Pokémon available in Scarlet and Violet that appears in Sword (or a game that has Marks).