During chapter three you will be tasked with burning supplies in Almuda, where you will encounter Albert, the trippy boss that represents Greed. The entire fight is rather indirect, as you wander around the halls waiting for one of the hallucinations to get attacked by the real Albert, who will come up behind them and drug them, then use his saw on them. You must avoid hitting the wrong people, as fake Alberts do quite a bit of damage, and you will be doing none to the real Albert, thus you must wait until you either see the real Albert trying to drug and dismember someone, or wait until you hear the screams of his victims. Then you rush Albert and pummel him with your fists, or throw organ containers at him. Continue the process, occasionally shaking your control to avoid getting attacked by him, and you'll soon defeat him.
Note that there is a possibility that Albert will flip out (..further..) and the camera will show him yelling at you with the prompt over his head. He will then start actively going after you, allowing you to spot him easier.