>>47642705Pokemon reincarnation.
You can reincarnate a pokemon to improve its base stats, but start it over at level 1. A pokemon can keep moves, abilities, or other abilities on reincarnation, but has to expend a currency earned from defeating other pokemon to do so.
You can build up relationship trees with your pokemon that offer specific bonuses (or drawbacks). Make two pokemon rivals, and their stats will increase when they are on the field together. Make two pokemon teacher and student, and the student can use the moves the mentor knows, that the student could also feasibly learn. Make two pokemon lovers, and their support moves will have double effectiveness on eachother, but they will suffer a permanent Taunt effect if their paired pokemon faints. Make two pokemon cousins, and they'll awkwardly try to mingle at gatherings before going to do their own thing, and try to find other girls to be cousins with, too.