Sound Test Mode
Press when you are death the C + D + S + T keys at the same time for the sound test mode.
Set Adjust
Also while the game is paused, you can press [SELECT] to have the sprites animate, or you can keep [SELECT] pressed and use the use the cursor keys to adjust the screen position.
Color palette
While playing the game press [SELECT] and while keeping it pressed, press [STOP]. Release the keys and you can adjust the color palette with the up/down cursor keys. Press [STOP] again to resume the game.
Level advance
Shoot the statues, from the normal comes an yellow ball which explodes and kills your enemies when you touch him with your ship. From the smiling statues comes the same ball, but after a waiting a bit it will turn black. Touch it now and advance some fields.
Weapon upgrade / extra lives
Shoot the statue with the big red eyes, it will strengthen your weapon, if you have weapon 0 you will get extra lives (4 max).
Various hints and tips
At the GAME START/CONTINUE select screen, hold down the numeral key of the B-weapon number you wish to start the game with, then make your choice. Pretty cool, huh?
Or (and this works for Zanac as well), don't fire at all a the start of the game, until the first 'spy' appears. Shoot it with your B-weapon, and it turns into a Randar (extra life).
Another one that works in both: just crash the 'blocks' when you're invincible. If one of them holds a 'P', you get the maximum upgrade (at least, when we're disregarding the 'colored face bonus' which doubles all your weapons)
Play the game unto area 2. Switch off your MSX (just as Big Boss told you to do). Switch it on again, holding the joystick in south-west direction. Choose "CONTINUE", and you'll start off in area 10
Keep catching B-weapon 6 upgrades. After a while (won't be until area 2 if you do it from the start, and yes, the game will get pissed off at first, ofcourse), your next shot will turn all the enemies on screen into Randars!
IIRC, area 4, 5 and 6 have one elve, and area 10 has two. If you touch it, it will instantly destroy the next base you face. You can't take them to the next area, so use them before that time
Keep your eyes peeled for the brightly colored 'faces'. They look like the 'normal' faces that yield the yellow 'smart bombs' (of which the more happy looking ones will become warps), but even more cheerful and colorful. I think they don't appear until area 3. Shoot them, and your A-weapon will be doubled (really nice if that was already at maximum) and your B-weapon will be maxed out
Not useful, but interesting: when you lose your last ship, hold down [SELECT] before the game over tune starts. You'll hear a totally different jingle