Natures
Lonely raises Attack 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.
Raises Attack at the cost of Defense, paying in a currency a physical attacker usually needs. It makes sense where nobody plans to take a hit anyway.
Flavor
Likes Spicy, dislikes Sour. This matters for Poffins, Pokéblocks and Berries: a Pokémon eats a disliked flavor reluctantly, and healing works worse.