>>42676904>mainline gameThat's where you draw the line? Well Meltan first appeared in Pokémon Go, but I understand what you're trying to say. When was the game where you have no proper wild encounters mainline though? They seem to go back and forth on that one. It's about as mainline as Gale of Darkness, which as someone pointed out, featured playable Bonsly. Pokémon Quest was done by Gamefreak, and that's not mainline, so clearly they're capable of developing the spinoffs themselves when they want. They can't be the deciding factor.
