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Super Plasma Bolt

Hold the UP arrow for about 2 seconds until you hear the "charge up" noise. Then press the fire key. You'll take a hitpoint of damage doing this.

Fireballs

Turn left and right in sucession about 6 or 7 times and press the fire key. You'll take a hitpoint of damage doing this.

Shield

Turn left and right in sucession about 6 or 7 times and press the jump key. You'll turn a different color, and a shield will appear around you. This lasts a VERY SHORT amount of time.

Invincibility

Hold the up arrow at least 2 seconds, then press the down arrow. You will flash and be invincible for a VERY SHORT amount of time.

Hex Editing

(This is version specific - backup first!!!)
For immortality, unlimited bullets & bombs: hex edit bmenace1.exe
Offset 61-64 change 2B 46 08 to 90 90 90
Offset 254-257 change FF 0E 08 44 to 90 90 90 90
Offset 117-120 change FE 0E 0D 44 to 90 90 90 90
Offset 468-471 change FE 0E ED 43 to 90 90 90 90