I had to reverse engineer this like a caveman! and this might just be specific to Wheel of Fortune (2010, Wii), I don't know if other Mii-based games use the same expressions.

Expressions:
0: smiling, eyes open
1: smiling, eyes closed (curved)
2: sad
3: sad with sad eyes
4: smiling, big eyes
5: smiling, dash eyes
6: O mouth