Press [Ctrl] + Y at the title screen. Set the controls for both players to be the same (for example, both on Joystick 1). Start a two player game. You will now control both Ernie and Bert a single joystick or the keyboard.
Level skip
Press the indicated key at the title screen to advance to the corresponding level.
Level
Key
1
A
2
E
3
I
4
O
5
U
WonderDweeb
Y
Second weapon
Press [Ctrl] during a single player game with player one using the Joystick. A second stationary weapon will appear in the middle of the screen. To cycle through the weapons, press player two's secondary key.