So I found yet another vertical scrolling glitch, that makes 4 different types now, there's probably more.
If you move down a ladder to the very bottom of the screen, sub-pixel, then press up, it will scroll you down ALMOST as if you had pressed down, except you will be standing during the transition, if you press attack or jump on the exact first possible frame once the screen has scrolled, you will attack or jump, if you don't, you will hang on to the ladder.
You might have to be half-way inside the ladder/wall as well.
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I see HUGE POTENTIAL for this:
If you could do the same thing but vice versa with up/down and top/bottom, you might be able to glitch from a ladder that normally goes to the over-world, instead to the room above it in the memory map!
Thus potentially every ladder that exits to the over-world could take you to a different room instead!
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another HUGE POTENTIAL glitch
I've discovered that, the damage you do is determined by what weapon you have selected when the hit is registered, not when you initiate the attack, this already has great potential with making regular attacks do special item damage.
Now note this glitch:
http://www.youtube.com/watch?v=BCjrB_08M4Y
Now note that the invincibility power up makes your turtle's weapon do AT LEAST enough damage to one hit every non-boss enemy, at least double that of scrolls, and potentially one hit bosses as well!
So if you haven't figured out what I'm getting at by now, it's basically to find a glitch that tricks the game into thinking you still have the invincibility weapon out, such as off-by-one errors with frame precise events that cause weapons to switch. If we could hack the rom to figure out how this was coded we could find a way to exploit the coding. Or we could brute force all possible ways.