Godzilla

Level select:
Press Up/Right + Run at the title screen. Then, hold Select and press Right three times, Up three times, Left, Left, Down, II within approximately four seconds.

All monsters:
Hold Up/Left + I + II on controller one and Down/Right + Select + Run on controller two at the title screen.

Monster select (player two):
Press Up/Right + Run at the title screen. Then, hold Select and press Right, Left, Right, Left, Right, Left, Up, Down, Up, Down, Right, II within approximately four seconds.

High speed mode:
Press Up/Right + Run at the title screen. Then, hold Select and press Up, Right, Up, Right, Up, Right, II within approximately four seconds.