Coda is the final character you unlock. She is essentially a combination of a few other characters. Her beat is twice as fast (you and the enemies move faster). You only have a dagger and half a heart. If you pick up any gold you die--and all enemies drop gold when killed. If you miss a beat you die (you basically can't stop moving).
There is no guide I can write for this. You will need to play hundreds or thousands of hours, and learn every nuance of this game. Only a handful of people can complete this. Spooty did this live at a speedrunning event, and it was insane (Run starts at 13:35