The screen scroll glitch only exists in the NES version of Zelda 1, and has to do with the way scrolling is coded. From a programming standpoint, Zelda Classic has absolutely nothing to do with the original, since Zelda 1 was written in 6502 assembly code.


EDIT: To plug my youtube channel in as a cheap a manner as possible, here's a video of me playing Zelda 1 on an emulator, and using the glitch to clip through blocks. https://www.youtube.com/watch?v=AhGhblQ66Ns