I think it would be fun if you could get the power ups that other characters use. Just imagine Mario using link's sword, or Simon Belmont using Mario's fireballs as a sub-weapon. This could also go along with the addition of levels from other character's games. You are playing in a Castlevania 1 level as Samus, hit a candle, and out falls the whip power up. This gives Samus the whip, or she gets to use the Castlevania sub-weapons.