When I played the game last time I wasn't aware that you can grab crabs! That intro is a very good way to show what your character can do.
Got to wave 11, crab-tan showing up just to get extra punch is very satisfying, new items help a lot (I think +HP was not present in previous demo?), sometimes punching upward won't flip the crab but nudge them off the platform.
I had fun and have no bugs to report. It's a little too hard past wave 10 so nerf pls (or spawn more items). Maybe you could also modify level a little between stages? Move platforms a little, fill one hole? Add a powerup that makes one floor solid for a fixed amount of time? I have to say that I've never played Mario Bros. long because levels stayed the same but palette swaps kept me mildly interested, so maybe also add that.
Anyway, I wait for Super Crab Puncher - get that one screen moving! :P