I liek the shadow arrow. Wouldn't it be awesome to combine fire arrows and bomb arrows? i'll leave it your imaginations to decide how awesomely destructive those could be
Thunder arrows would be cool too. Same effect as fire arrows, but could be used for solving electrical puzzles, especially if the next game is futuristic. Anyone played Tales of Symphonia? Think about infultrating the desian bases and using the electrical sorcerer's ring.