Natures
Hasty raises Speed by 10% and lowers Defense 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.
Speed at the cost of Defense. A pick for mixed sets that do not count on surviving a hit anyway.
Flavor
Likes Sweet, dislikes Sour. This matters for Poffins, Pokéblocks and Berries: a Pokémon eats a disliked flavor reluctantly, and healing works worse.