Mawile is based on the futakuchi-onna; a Japanese Yokai [or demon spirit]. Basically, when a woman was fasting, if she deprived herself for long enough a second mouth would grow out of her head and start screaming obscenities and demand food to nourish her body. Eventually, if she continued to starve herself, her hair would branch out another serpent like mouth and the two branches would work together to start consuming food without the permission of the woman who was fasting.
The purpose of choosing Mawile to represent Cooking Mama is deeply tied within the roots of the Pokemon's inspiration. It is relevant for more reason that simply being humanoid and having an "M" in its name.
Oddish is there simply because it looks like a vegetable, though I would also like to believe in the fact that cooking friends would make quite the "odd dish".
