Now that they’ve changed how you get eggs in Pokémon Scarlet and Violet, that has lead to some experimentation. Day Cares and nurseries have been replaced with picnic baskets as you get the Pokémon you want to breed together in your party, maybe make a sandwich to increase your chances of eggs, and… wait. But Austin John Plays has found a method that involves having three Ditto and three Pokémon that can all breed with each other (in his example, the three Paldean starters: Sprigatito, Fuecoco, and Quaxly) and discovered that the egg rate came out higher when you had 3 Ditto + 3 partners, vs. 1 Ditto + 3 partners vs. 1 Ditto + 1 partner. I don’t know how much of this is logical or obvious as the game has only been out for a month and I dodged leaks like Neo in the Matrix with bullets but it’s an interesting watch and I’ve been using this method to great effect (lots of eggs that is; no shinies yet).
A triple Masuda breeding method in Pokémon Scarlet and Violet
You get an egg, you get an egg. Everybody gets an egg!