For invulnerability in this game, use the DOS utility DEBUG. First backup your game to be edited, then type the following from the DOS prompt:

For the CGA version of this game, type:

ren roller.exe cheater.cht
debug cheater.cht
e 1e8d 90 90 90 90
e 31c7 75
Then type:
w
q

For the EGA version of this game, type:

ren roller.exe cheater.cht
debug cheater.cht
e 1e62 90 90 90 90
Then type:
w
q

Then rename CHEATER.CHT back to its previous name.