Amok

All these are typed at the password screen:

Mission 2, Phase 1: CBYXYC
Mission 3, Phase 1: XABXAB
Mission 3, Phase 2: AZCBXC
Mission 4, Phase 1: YYBBCY
Mission 4, Phase 2: BAXCXX

Enable Level Select: ZZZCYX
Show Credits: ZAZACC
Invincibility: BABYXX.
Rapid Fire: YAYAYA
[YAYAYA]: Unlimited ammunition and something else?
[ZABCXY]: I wonder what this does!
[BABYXX]: You don't die when the energy reaches zero.
[XXCXXX]: Unlimited ammunition and something else?
Level select: [ZZZCYX].
Credits: [ZAZACC].

This game is developed by some Danes and published in the USA.
Choose the code that shows the credits to read some special Danish comments...!