Buffy The Vampire Slayer - Platform: XBox
      
Unlock Multi-Player Arenas
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At the Extras Screen, press 
Y, Y, White, Black, Black, 
Y, Y, Y, Y, Y, White, Black.

Unlimited health
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At the Extras Screen, press 
Y, White, Black, Black, White, Y, Black, Black, Black, Y, Y, Y. 

Slayer power
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At the Extras Screen, press 
Y, Y, Y, Black, Black, Black, Y, White, Black, Black, White, Y. 

Unlock Multi-Player Arenas
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At the Extras Screen, press 
Y, Y, White, Black, Black, Y, Y, Y, Y, Y, White, Black. 

Play as Dark Buffy in arena mode
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At the Extras Screen, press 
Black, White, Y, Y, Black, Black, White, Black, Black, 

Arena Mode ( Multiplayer) 
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Enter the "extras" menu 

Y-Y button 
W-White button 
B-Black button 

Press: YYW-BBY-YYY-YWB