1) Dig up the Gulkave tape (it ain't a ROM game, right?)
2) Smash it into your tapedrive and boot your M$X
3) Load the game
4) Select 'hard mode' from the title screen
Unfortunaly, you will start the game in 'normal' or 'easy' mode, as there's no level select option on the title screen ... you can only choose between 1 or 2 players ... so, what's the trick ???
1: rename yourself to mars2000you
2: create blueMSX cheats for Gulkave
3: test the cheats by extensively playing the game
4: find out that completing the game unlocks hard mode?