Full body awareness
First person games where when you look down you see your body (legs, pelvis, torso, etc.) instead of nothing (just hands/arms are not enough). Not including cases limited to scripted sequences, cinematics, or others where player control is limited.
Alternate name: Self-awareness
The first video game about Full body awareness was released in 1984.
The most 2D games can do is have separate screen depicting the character's lower body from an angle (for whatever purpose I can't imagine), this is however not very spectacular of them other than having a screen with specific graphic content and is not covered by this tag. For 3D games however this is unusual and technically somewhat challenging.
Example from Mirror's Edge: