The reason behind the dual facial expression that contradict each other is because half of his face litterally cannot react. The mascot head he's TFing into is static, which means it doesn't have any face muscles.

He is transforming into that mascot (but with a red nose) :

https://twitter.com/gyu_usi/status/1481571537698582533?t=0_ddq4XexsmXOa0L6GSMLg&s=19