Open a hex editor

Expand the rom to 2MB
ie add 100000 bytes in hex after the end of the rom, this will add 1MB to the rom

go to 039AC7 and overwrite
9C E3 02 AD 01 03 -->
with the new
EA EA 22 00 80 3D

go to 1E8000
and write-in new code (previously empty)


039AC7,
9C E3 02 AD 01 03 -->
EA EA 22 00 80 3D

1E8000, write new code by Zarby
A5 F0 29 01 F0 06 A9 06 85 2F 80 20 A5 F0 29 02 F0 06 A9 04 85 2F 80 14 A5 F0 29 04 F0 06 A9 02 85 2F 80 08 A5 F0 29 08 F0 02 64 2F 9C E3 02 AD 01 03 6B



This also means you will be able to change direction while holding/charging the sword, which debugs entering into certain caves, since you otherwise (original code) can enter (and thus exit) too high up, if you enter sideways.