It's strange... something is missing here, i never saw a trick like this on the Neo-Geo, the "dual jump" trick it is not a program error, i enjoy this game very much but, what i think is that the game was not polished (maybe a tight deadline?)... I dont know...
Updates:
ELTA: jumps more than two times (max here 4 times)
SHINOBI: jumps more than two times (max here 3 times)
DRAGON: I BELIEVE DOES NOT WORK (???)
WATERMAN: jumps AND jumps AND jumps AND jumps (max here +-8 times?)
SAMURAI: I BELIEVE DOES NOT WORK (???)
RAIJIN: DOES NOT WORK (???)
POSEIDON: jumps more than one time (max here 2 times)
*The trick varies according to the character:
ELTA: JUMP, FIRE.... JUMP,FIRE....JUMP, FIRE.... (slowly)
SHINOBI: SAME AS ELTA
WATERMAN:JUMP, FIRE. JUMP, FIRE. JUMP, FIRE (frenetic)
POSEIDON: its hard to do but it works.... Elta style
Here is the "easter egg":
http://www.youtube.com/watch?v=IKDW0jKXoyE