Astro Boy: Omega Factor
Astro Boy: Omega Factor
The game went through massive changes when it was ported from Japan to the US. The Japanese version only has Easy and Difficult difficulty settings. The International versions removed these in favor of Normal and Hard, with Normal as a re-balanced version of the original Difficult. The international versions also add a health meter for the bosses, language selection, a couple new enemies, adjusts some of the level layouts, and fixes some of the slowdown.
Contributed by Mr. Kite
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There is a secret room in stage 6, the Pyramid, in which a unique enemy can be found. It appears to be a white octopus with a pink ribbon, and will drop a health pickup if attacked.

The character is called "Ebiinu-kun", and was created by background designer Zoruge Ichizo. Ebiinu-kun was later featured in a manga he wrote and illustrated called "Sol Pride Ebiinu-kun".
Contributed by EpicSato
The music that plays in the last scene of the game is the same music that plays in the last cutscene in Gunstar Heroes, also developed by Treasure.
Contributed by Gors