The general idea rn is Pokemon with deep lore/attachments to Legendary/Mythical Pokemon and generally ancient lore based Pokemon! For example
Phione - "Spawned from Manaphy"
Carbink - "Baby/Progenitor Diancie"
Unown - "Ties to many ancient legends" (Plus that one movie where they literally spawned an Entei)

Not commited to toooo much more atm except maybe Claydol!