From the start go right up the ladder and jump on the moving plattform continue left.

The next screen is a vertical tunnel with some flying dudes.

Jump down and enter the 4th entrance on the right.

There is some knight demon dude. Kill him he gives you 12 credits.

Exit the screen to the left again and re-enter.

Kill that knight dude until you have 999 credits.

Exit to the left again and jump down to the next entrance.

Take teh entrance and just fall down into the gap to your right.

Move left and you are at the very beginning of the game.

Go to the machine and press up

Upgrade your warrior to kick some bad guys.
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If you are to lazy, try if it works with my save game.

In the game menue go to the password section and use this one:

NIT-T1Y-JNQ-XKG

You will gett the password achievement for sure, I don't know if it unlocks all the others.