Here are a few ideas:
Wind Waker?:
Yes, a windwaker frm LoZ: TWW. Playing notes by pressing it either hitting a block or somethin'.
RPG Health Bar:
I realize there are already hacks like that. But I'm thinking of SP, HP, 999 money counter, level up display, battle overworld and more! But since I fail at ASM, I can't do that.
Space POP:
There are sky POP and underwater POP. But with the sprite that Carol used fo the spaceship level and a bit of tweaking, we can make a Space POP!
Water that drains your money:
There is water that drains time, there is water that reveres your control and time that drains your coins. But what if we had water that drains your coins?
SPM Flip Gauge with other uses:
SPM Flip Gauge can be used to determine your time left underwater, the time of he level or the dragon coins.
Super Mario Advance: SMW "Death Cry":
As someone else suggested, someone should rip that "Mamamia!" from the GBA SMW.
SMB3 Style Secret:
You know the secret flute in the 2nd level of SMB3? The one that you have duck long enough to go behind the level? We should implement that into a SMW Hack.
M&L:BiS Bowser Help:
Like M&L: Bowser's Inside Story, we'll have Bower help. Unlike M&L: Bowser Inside Story, we'll have to make it into a platformer or an RPG.
SMB1 Exact Replica:
Same replica meaning, same graphics (also Mario) and same flagpole end.
Shoot-em-up game, once again:
This should be some kind of mini-game.It has to be hard to get to and do. With a specific amount of score, you get a better reward, like this:
5,000 - 30 coins
10,000 - 50 coins
50,000 - 99 coins
100,000 - 1-up
150,000 - 2 1-ups
250,000 - 3-up
500,000 - Secret Level
1,000,000 - 3-up, secret level and instant warp to Bowser
5,575,230 - Secret OVERKILL power-up (Make sure the mini-game is hard)
Overkill Power-up:
You guys know what it is. A starman that gives you the feather and a fire flower at the same time with sumo bro fire that falls from the sky and kills all the enemies on-screen when you have 50 seconds left on the time limit. Make it like you have no chance to get it.
Race of Heat:
You have to get bubbles to stay warm undrwater. But ou only have limited time getting to the goal.
Those are all I have for now. Bye!