Here’s a great way to farm Yellow Essence during chapter two. After ridding the bridge you encounter of all of the archers and acquiring the Crystal Skull there, you will have to continue down another wooden path. This will lead to a pair of chasms that you have to swing over to get to the save point. Below that is a lower walkway full of enemies. Kill them all, and then scale a nearby ladder to reach the upper area again. When you go back down, the enemies will have respawned. You can kill them again to grab their Yellow Essence, climb back up, jump back down, repeating this ad infinitum to get all the Yellow Essence you want.