so that buddy update is apparently coming out later this fall
if a pokémon is small enough it'll ride on your shoulder, while bigger ones will walk next to you, and every time you walk a certain distance (which might be different depending on the pokémon?) it'll give you one of the candies for its species, so presumably if you can't find very many of a specific pokémon you can make it your buddy to get candy easier
you can change your buddy at any time so it's not a huge decision like picking a team, but it'll reset the reward distance counter every time you do
honestly I'm super excited to have a magnemite on my shoulder