Jevon's Control Mode:

 During play, pause the game and  enter  the  options  menu.  Highlight
 "Customize  Control"  and  press  R, R, L, R, X, Y, Z, X, Y, Z in  one
 swift motion until you see a faint message appear behind the text from
 the option menu. Jevon's Controls should now be activated. 

 Note: This control mode requires an analog controller. 
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Monster Control Mode:

 During play, pause the game and  enter  the  Options  menu.  Highlight
 "Auto  Targetting" and press R, R, L, R, X, Y, Z, X, Y, Z in one swift
 motion until you see a faint message  appear  behind the text from the
 option menu. Your weapons will become more powerful, but only one type
 of weapon will 'upgraded' on each stage. 

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Nightmare Mode:

 To play in Nightmare mode, choose the fourth episode and fall into the
 pool of  water  near  the entrance. While you are sinking, strafe left
 until you reach land, then  walk  toward  the doorway.  There you will
 find a secret slipgate that leads to Nightmare mode.