Infinite Life Of The Gods and Elixirs
At the beginning of Chapter 7, there is a glitch that allows you to get an almost unlimited supply of Life Of The Gods and Elixirs over the course of the game, as long as your have access to Tairon's Monastery Annex Save Point. When your first pick up the two chests near the save point in Chapter 7, they will respawn later in other missions. This gives you an almost unlimited supply of Life Of The Gods and Elixirs. This only works for Ryu.
Easy Essence
In Chapter 12: The Aquaducts, go in the room where you are attacked by the oversized beetles. Use the Art Of The Imzana Ninpo as many times as possible to get about 5,000 Essence.
Easy Orbs
In Clock Tower Plaza, there is a stairway marked with blue. Go up the stairway and around the corner. Three soldiers will appear. Kill them to get a maximum of 300 Orbs, if they all drop yellow. This is not much, but if you kill the first two quickly and then press Triangle (default) to do your charge attack, absorbing the Orbs from the enemies you just killed, and unleash it on the remaining person, you can get about 1,000 Orbs. Only a few seconds are required each time, and you can do it as many times as desired.
In Chapter 7: The Monastery, after putting the Book Of Eons on the pedestal in the monastery, the tomb opens up and you are dropped downstairs into a dungeon with four "Will-O-Wisps" floating a ninja body, a chest, and a save pedestal. Stand just at the edge of the small pathway before the first "Will-O-Wisp". You can charge your heavy attack (Triangle) and hit the one closest to you with it. Then, two more will try to attack you, and you may get caught in the super. This can produce up to 1,500 Orbs per visit, as many times as desired. Go back up the ladder then back down, and charge attack again for easy and quick money.
In Chapter 7: The Monastery, as you wind your way down the spiral ramp (with the giant dinosaur skeleton), you will find what appears to be a giant plug in the floor held up by three huge chains. It is called the "Econtra Babel Specus". There is a shop on one side. On the other side is a corridor which leads to a "T" shaped room. As soon as you come around the left corner, prepare your ultimate technique with Triangle. Wait for the second power burst before launching it on to six "Will-O-Wisps" in a row. Try using the "Lunar-stage 2" because of its upwards tornado-like effect. As soon as you have collected the Orbs, keep going left towards a ladder at the end of the room. Hit your ultimate again because there are seven more "Will-O-Wisps" coming up the ladder. As soon as you have collected the Orbs, go back the way you came. You do not have to go all the way out again; just about halfway up the corridor. As soon as you turn the corner they will respawn. You can repeat this as many times as desired. Since the store is in the next room, you can make enough money to buy whatever desired through the rest of the game. Note: This was done in Normal mode with Ryu.
In Chapter 12: The Aquaducts, when you reach the point where there is a save point near the main door (which leads to a huge statue of the girl, with three water weights around her), save the game. Turn around and face where you came from. Take a few steps and turn to the left path. You will see a small door, like an elevator. Go in there, and press L2 to display your Karma. The first time you go in, kill all the Scorpion-looking things and remember the total number killed. This number will appear on your Karma display. Return outside and save the game if desired. Go back in, but do not kill all of them. Leave when there are two to four of them remaining. Go back in and they will appear again. Repeat this as many times as desired.
Defeating the motorcycle troops
Use the Guillotine Throw to pull them off the bikes. If you do not have that technique, another good way is to jump around frequently, trying to avoid being hit, and to attack them with the projectile weapon of your choice whenever you land. Note: The motorcycle soldier with the sidecar cannot be grabbed with the Guillotine Throw.