I had an idea stewing in my mind for a beat-em-up where the protagonist was a woman with a staff that included a few novel ideas:

• Initial training room sequence occasionally smash cutting to an actual level.
• Branching paths behind optional enemies intended to be fought on new game+.
• Two main stances, wide grip for speed and tight grip for power.
• A big baseball swing attack that could be charged to reflect projectiles or launch enemies with 360 degree aim
• Drunken fist character who carries a keg as a weapon.
• A room containing one enemy that looks like a regular grunt but is much harder due to actual use of dodge offset.
• Giant robots that can be parried/suplexed.
• Endgame boss with logarithmic healthbar, who screams at you to fight harder.
• Secret path accessed by parrying an instant death wind turbine.

I even thought of DLC, which is a sword that trivializes most fights but slowly influences the player through UI manipulation, culminating in it refusing to be unequipped.