Unlock Extra Stage

On the last level you have to face two people, a boy and a girl. If you beat them you unlock that guy and his mansion. That means when you play against another player you can pick that guy and have a shootout in his mansion.

Unlock Fit Dog

Finish stage 6.

Unlock Infinite Adrenaline

Finish stage 5.

Unlock Infinite ammos

Finish stage 4.

Unlock Normal Challenge mode

Complete game in Normal.

Unlock Super Deformed Mode

Finish stage 2.

Unlock Supercop mode (hard difficulty)

Complete game in Normal.