Your Tenchu Z Cheats

Hint - Bossploitation
The last two bosses on Mission 50 are tough, but easily fooled. Once you find where the first of two bosses are (in the palace cut-scene), head east, towards the river.

The first boss will come down the stairs and approach your assassin. With luck, he will step off into the water and die. If not, push him off (easy) with a few sword blows). The second boss is killed in a similar manner.
Hint - Roll Your Ass
Okay, okay, so you all know walking makes less noise than running in the game; however, sometimes you just need that extra speed running to get up close to enemies.

Rolling makes your character move at the same speed as running, but at a greatly reduced noise (compared to running). It's not completely quiet as crab walking, but it is not as loud as running across crickety floorboards. The best part: your assassin can change directions while rolling, so roll like Link if you need speed and stealth.
Hint: Bossploitation
The last two bosses on Mission 50 are tough, but easily fooled. Once you find where the first of two bosses are (in the palace cut-scene), head east, towards the river.

The first boss will come down the stairs and approach your assassin. With luck, he will step off into the water and die. If not, push him off (easy) with a few sword blows). The second boss is killed in a similar manner.
Hint: Death Money

Each time you die or lose a mission, you will get some money. If you die/fail over and over again, you can accumulate a huge amount of money.

It’s easy, regardless of game difficulty, to score a Ninja 5 rating on each mission in the game. If you go undetected, uninjured, and use no items, you’ll get 300 points right off the bat towards your rating (100 points for each). Since you need 900 points total to reach Ninja 5, you’re only 600 points away if you get the initial 300 points. Stealth kills are worth 120 points each, so killing five people by stealth means will earn you the points you need, though stealth killing a boss enemy is worth 300 points. Regardless, with these numbers in mind, scoring Ninja 5 on every mission is easy.

If you're very patient, you can level-up your character by playing and replaying Training Mode over and over again. It takes a lot of time, but you can theoretically max your character out with enough time spent in Training Mode, to the point where your character could get through the hardest difficulty in-game with no issues.