The following yellow essence exploit can be completed on the game’s very first chapter, and is especially useful when playing on Master Ninja difficulty. Before and after crossing the bridge, you’ll deal with enemy ninjas (it’s the bridge where the first God of Life and a treasure chest can be found). After you cross the bridge, defeating ninjas as you go, head towards the middle alley that brings out two more ninjas on foot and another two ninja archers. Run back and charge up to Ultimate Level 2. Continue to run back and forth, and the ninjas will keep respawning and coming at you. If you have the skill, getting away with $40,000 while having 50%-75% of your health still available to you is a possibility.

Another technique from davidlaughs.

There’s a walkway below an area where you have to swing across a pipe. You’ll run into two more, and then reach a save point. This is where the exploit can be found. Drop down below the save point and a group of five bad guys will attack. Kill all of them, climb up the ladder and head to the first pipe. There, drop down and you’ll be confronted with another wave of enemies. Repeat this process over and over again for as much essence as you want.