Natures
Relaxed raises Defense by 10% and lowers Speed by 10%. It is applied at the very end of the formula, after IVs and EVs, so the higher the stat, the more the nature gives and takes.
Defense at the cost of Speed. Good under Trick Room and with Gyro Ball, whose power grows the slower the user is.
Flavor
Likes Sour, dislikes Sweet. This matters for Poffins, Pokéblocks and Berries: a Pokémon eats a disliked flavor reluctantly, and healing works worse.