Natures
Naughty raises Attack by 10% and lowers Sp. Def 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.
The riskiest of the Attack natures: it lowers Sp. Def, the stat physical attackers usually have at its weakest.
Flavor
Likes Spicy, dislikes Bitter. This matters for Poffins, Pokéblocks and Berries: a Pokémon eats a disliked flavor reluctantly, and healing works worse.