Copy/paste de un faq (
http://www.gamefaqs.com)
Chris Zawada escribió: Ninja Gaiden --> Gather a total of 50 Golden Scarabs, and return them to
Muramasa. He will hand you a Ninja Gaiden cartridge disk.
>> NOTE: You do NOT have to collect all 50 scarabs during
all 16 chapters. As a matter of fact, your scarabs
are carried over into a next game (of same
difficulty). Simply collect 50 in consecutive modes,
and Muramasa will give it to you as a reward. Any
scarabs you gathered in the previous game will not
appear, so you'll have to find the ones you missed.
Ninja Gaiden 2 --> After receiving the original Ninja Gaiden disc, go to
the Clock Tower Plaza of Tairon City. Get on the ledge
above the multicolored door (it's the switch that unlocks
the multicolored door). Pull out your bow, aim, and shoot
an arrow at the face of the Clock Tower above. A treasure
chest will appear on the building opposite of you. Jump
down, head up via the doorway at the bottom, and the chest
contains a Ninja Gaiden 2 disc.
Ninja Gaiden 3 --> Before getting this, you must receive the Ninja Gaiden 2
disc first. Go to the Peristyle Passage, which is in
Chapter 10. It's right before the boss fight. Go to one
of the broken pillars, and you should be able to find a
scarab up above. The Ninja Gaiden 3 disc is located there
now. If you're having trouble getting this one, refer to
my Chapter 10 walkthrough to receive it.
O sea:
Ninja Gaiden 1: consigue los 50 escarabajos de oro
Ninja Gaiden 2: Una vez tengas el NG1, vete a la ciudad de Tyron, y metele con el arco a la Torre del reloj, desde la puerta con el simbolo multicolor.
Ninja Gaiden 3:Una vez tengas el NG2, podras conseguir el cartucho del 3 en el 10 nivel, justo antes del enemigo de final de fase. Por lo que dice el faq, deberia estar en lo alto de una columna (antes habia un escarabajo)
ala.