Fish Farming - Yellow orbs
Once you reach the top of the tower in CH 18(The Core), save your game. Use the black floating panel next to the save point, which will refill your life and Ninpo. Equip your "Art of the Fire Wheels" spell, and go to the top of the ramp you just climbed. Use the Ninpo and simply stand there while the fish jump up and die on your fire shield, one after the other. You can repeat this as needed for yellow orbs.

Easy Essence
When you have the Left Tablet and are heading back to put it in with the others, you will go over the drawbridge. When you get across the drawbridge there will be 3 purple monsters with large swords. You will need to kill them and get the special box. Use the Unlabored Flawlessness or the Dabilahro to kill the monsters. Try to stay a little bit back and use triangle to power to maximum.
When the monsters get close enough just let go. This takes about 3 hits on each. Then either go down the stairs or jump off the ledge to the save point below. Save your game, then head back up the stairs and kill the purple monsters. They will continue to put out yellow essence as long as you kill them. Have at it!

Airship $$$ Money
When you get to the airship level and come to a room where many soldiers will come and attack you. If you’re in need of money, this is a good place to get it, because you can fight everyone in the room, exit, and then reenter to respawn the enemies. Repeat as much as you like for $$$ Money.

Target Practice For $$$ in Chapter 2
Step 1: From Hayabusa Village in Chapter 2, after you enter the first house go to where the store statue is and you will exit that map.
Step 2: Ryu will be attacked by a couple of magic ninjas and samurai. Once you defeat them, you will notice a small board lying on the ground.
Step 3: In the distance you will see 3 targets near a fence at a dead-end. Now it is time for a little work with your bow. Shooting these 3 targets with a bow will give you Gold, Health, and Ninpo energy. You must be standing past the loose wood board at the corner of the house Ryu entered in order for the rewards to spawn. You can hit the money target 5 quick times, collect the gold and keep buying arrows to replenish your stock. This will only work a few times before they stop awarding you stuff.

Mission Mode
Just defeat Doku in the second chapter of the game to unlock Mission Mode.

Golden Scarab Items (Master Ninja Difficulty)
As you find Golden Scarabs in the game, Muramasa will reward you with the following items specified to how many you’ve found…

1 Golden Scarab	Smoke Bomb
5 Golden Scarabs	Elixir of Spiritual Life
10 Golden Scarabs	Great Spirit Elixir
20 Golden Scarabs	Great Devil Elixir
25 Golden Scarabs	Smoke Bomb (II)
30 Golden Scarabs	Ayane’s Ration
35 Golden Scarabs	Fragrance of Dayflower
40 Golden Scarabs	Ayane’s Ration Bundle
45 Golden Scarabs	Fragrance Hydrangea
49 Golden Scarabs	Plasma Saber MkII
50 Golden Scarabs	Dark Dragon Blade

Golden Scarab Items (Normal Difficulty)
As you find Golden Scarabs in the game, Muramasa will reward you with the following items specified to how many you’ve found…

1 Golden Scarab	Life of Gods
5 Golden Scarabs	Armlet of Potency
10 Golden Scarabs	Lives of the Thousand Gods
15 Golden Scarabs	Spirit of the Devils
20 Golden Scarabs	Dabilahro
25 Golden Scarabs	The Armlet of Celerity
30 Golden Scarabs	The Armlet of Benediction
35 Golden Scarabs	Great Spirit Elixir
40 Golden Scarabs	Armlet of Fortune
45 Golden Scarabs	Jewel of the Demon Seal
50 Golden Scarabs	Plasma Saber MkII

Golden Scarab Items (Very Hard Difficulty)
As you find Golden Scarabs in the game, Muramasa will reward you with the following items specified to how many you’ve found…

1 Golden Scarab	Art of the Inferno
5 Golden Scarabs	Spirit of the Devils
10 Golden Scarabs	Art of the Ice Storm
15 Golden Scarabs	Jewel of the Demon Seal
20 Golden Scarabs	Spirit of the Devils (II)
25 Golden Scarabs	Jewel of the Demon Seal (II)
30 Golden Scarabs	Armlet of Fortune
35 Golden Scarabs	Jewel of the Demon Seal (III)
40 Golden Scarabs	Art of Inazuma
45 Golden Scarabs	Spirit of the Devils (III)
50 Golden Scarabs	Dark Dragon Blade

Golden Scarab Items (Hard Difficulty)
When you find Golden Scarabs, Muramasa will reward you with the listed items specified to how many you’ve found:

1 Golden Scarab	Counter Attacks (Technique Scroll)
5 Golden Scarabs	Izuna Drop (Technique Scroll)
10 Golden Scarabs	Guillotine Throw (Technique Scroll)
15 Golden Scarabs	Windmill Shuriken
20 Golden Scarabs	Wooden Sword
25 Golden Scarabs	Dabilahro
30 Golden Scarabs	Armlet of Celerity
35 Golden Scarabs	Spear Gun
40 Golden Scarabs	Armlet of Benediction
45 Golden Scarabs	Armlet of Fortune
50 Golden Scarabs	Dark Dragon Blade

Hit Muramasa for free yellow essence
Visit Muramasa’s store and score some free yellow essence from him simply by attacking him. Try attacking him with a weapon like a nunchuck, and he’ll begin dropping his yellow essence. But don’t over do it! If you hit him too many times, he’ll fall due to his injuries and you will get a Game Over. Save your game so you can see how many times you can hit him before he dies and get the maximum amount of yellow essence from him.

Easy $$$ Money
While in the 4th chapter [Imperial City Infiltration], go to the shop that is near the town gate. A guy will be sitting there, and you can throw Shurikens at him. Each time you hit him, you get an item worth 100 yellow essence. Do this nine times, but not a 10th , or you will kill him. Now, leave through the gate, come back, and try again. You can make 900 yellow essence per visit.

Yellow Orb Exploits
Method 1:
There is a way to get unlimited yellow orbs. You have to play chapter 3 Skies of Vengeance.
Get the key card on the lower level.
Save your game by going down the one of the spiral staircases off the Main Deck.
Go back to the beginning of the game.
At the end of the hall in the Living Quarters there is a door that requires the key card. Make sure you have a few Elixirs of Spiritual Life before you enter. Kill as many enemies as you can without dying, then exit through the door.
Save your game, restock your elixirs at the shop (it is located at the other spiral staircase of the Main Deck) and repeat. Once you have all the upgrades that you can purchase at this level, you can just stock pile as much Yellow Orbs as you like.

Method 2:
This method is for at the end of Chapter 13 where Ryu must swim through the aquaducts to reach the platform leading to a battle with Lord Doku.
You can farm some yellow orbs here:
Save here and equip the Spear Gun. Before riding the platform to the battle (or even just after, at the start of Chapter 14), swim back under the passageway and into the lift room (the one full of Shark Creatures).
Each monster is worth 1000, so you can collect about 6000 each time you go through the place. Swim just to the bottom of the tunnel and then back, allowing the creatures to respawn, then repeat. Do this for a few minutes, and then be sure to visit the conveniently placed Muramasa's shop statue to fully power up all your weapons and stock your inventory.

Bonus Costumes
Ryu Classic : Complete the game on Normal difficulty.
Ashtar Costume : Complete the game on Hard difficulty.

Extra Difficulties
Accomplish the following requirements to unlock extra difficulty levels:

Ninja Dog	Die three times consecutively.
Hard	Complete the game on Normal difficulty.
Very Hard	Complete the game on Hard difficulty.
Master Ninja	Complete the game on Very Hard difficulty.

Collectors Edition Extra Missions
Enter the following button-tap cheat code on the Missions screen:
UP, DOWN, LEFT, DOWN, RIGHT, UP, SQUARE