Infinite Shuriken

In the OPTIONS menu, set the S.E., to "shuriken" then set the shuriken count to "00." Wait...wait...yes, wait  like you did in Revenge of Shinobi...and...BLARP! There you are! Infinite Shuriken.

Invinciblity

In the OPTIONS menu's music selector, press B to play these songs in this order: HE RUNS, JAPONESQUE, SHINOBI WALK, SAKURA, GETUFU.