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In the Arcade version, if the player presses shot-3 six times, start eight times, then shot-3 again before the stage name disappears at the start of a stage, a hidden credit appears for "Yu Suzuki", the games programmer.
Contributed by ProtoSnake
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In the SEGA Master System version, if you enter "ERI" in all of the highscore places, a secret message will appear. The message reads:

WORNDERFUL FANTASTIC

YOU, SMART GUY


PLEASE SEND US YOUR THOUGHTS
TO THIS GAME. WE'LL ANSWER A
LETTER WITH SOMETHING TO THE
FIRST TEN PERSONS.

SO, FORGIVE US, IF YOUR LETTER
IS OUT OF TEN, WE CAN'T REPLY
TO YOURS.

BY THE WAY, CAN YOU SEE WHY
YOU CAN FIND THIS MESSAGE?


SEGA ENTERPRISES LTD.
R,D NO.4 "SPACE HARRIER"
1,2,12 HANEDA, OTA KU
TOKYO, JAPAN 144

It will appear for 50 seconds with the "Haya Oh" song played over it and afterwards players will be taken back to the title screen.
Contributed by KnowledgeBase