Some of the things I was thinking was, should the player slowly gain abilities as the game progresses? Should they be unlocked with a money system? How long should the game be? Any suggestions for traps, levels, things like that, let me know!
In my opinion, if the story of the game takes place on differents locations, I prefer that the player gain abilities as the game progresses. Otherwise if the game progresses in the same area but with more difficult missions, I think this should work better with the "money system".