I'd really like to get rid of the Challenge Mode in my hack. I'm sure it can't be that difficult to do, but I can't find any tutorials anywhere (even using the search bar). Just to be more clear, I'm not talking about toggling which areas use Challenge Mode and which ones don't, I'm talking about disabling it entirely, meaning it can't be accessed.

Does anyone have any idea how to do this, or is this still something nobody's figured out yet?
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New Super Mario Bros. Empire | World 1 demo

You could patch an action replay code that always forces the "on/off" variable to be off....

This is probably incredibly non-relevant by now, but here's how to do it if you still need to:

Decompress overlay9_8.bin using some old edition of NSMBe (the current one can't decompress)
Extract it
Open in hex editor
Find the hex values on the left and replace them with the ones on the right:

000094E5080050E3 -> 000094E5FF0050E3 <- this makes the last key of the sequence be a non-valid button
3300A0E30010A0E30030C2E5 -> 3300A0E30010A0E30000A0E1 <- this disables switching on the challenge mode entirely, just in case

Save, replace.

Technical notes:
02085A10 <- variable which turns the challenge mode on (1 if on)
020D05D0 <- Place in RAM where the above happens (both US version of the game)