Go to the option screen and play these songs in the following order HE RUNS, JAPANESQUE, SHINOBI WALK, SAKURA, GETUFU this cheat will make you invincible.

At the options screen go to S.E(sound effect) and select SHURIKENS then go up the options screen to where you can select the amount of SHURIKANS and set it to 00, then wait a little while and they will become unlimited.