Death To The Helicopter
You know that annoying helicopter that is one of the first few bosses? It can be easily defeated without having to repeatedly jump. All you have to do is get under it and double jump, dash, slash. You can dash after each hit with your sword and get in multiple fast hits.
The many faces of Shinobi
If you beat the game once and collect thirty talismans, Hotsuma's brother Moritsune becomes available. Moritsune is stronger faster, and less hearty than Hotsuma. Akujiki feeds off him more quickly. If you beat hard mode with forty talismans collected, you will unlock the OG - Joe Musashi himself. While he isn't as strong in sword play as the brothers, he can throw shurikens like no bodys business.