Go into your Blood Omen 2 DATA directory (ie: "D:\games\blood omen 2\data") and locate the game.erg file. You can open it with notepad.
Locate the following line:
"-BO2 Kain Debug Flags\kain's invulnerable"=1
Change it to:
"BO2 Kain Debug Flags\kain's invulnerable"=1
Save the file and load the game. You should now have god mode.