>>52659245Not only that, they're also just four strong Pokemon and easily accessible for clearing the main campaign, even if you can't fully evolve them.
Four extremely common gym leader/elite four types. (Fighting ,Rock, Psychic, Ghost). And their lines are almost always slotted into Gym Leader/E4 teams if they can be too.
I consider them a pseudo-quartet of the dev's dex slot-ins, most of the time they're always going to be in together. Though this time with SV, it's just the Gastly line.
