Very cool! It's funny these are button combinations like classic game cheats. What would the Konami code or Up-Down-Left-Right-A+Start give, lol?
Hehe, definitely brings me back to being a kid in the 90's!
As far as the instructions go, Up-Down-Left-Right-A-Start would translate to the ld sp,hl
The Konami code would actually be 3 instructions: ld b,b
; add a,b
; and ld l,e
And yeah, both would cause the game to NOP slide to its (probable) demise.
Imagine using 8F in 1996/7
Oh man, it's crazy to think what people would have come up with back when the GameBoy was in its prime. With all the GB devs with gbz80 experience, it would've only been a matter of time before a few of 'em made some truly unique and crazy stuff with it. =')