When you're in the dark spyro part, just keep running. When he shoots the eye beam, just change direction of running to opposite way. When he starts to spin creating that tornado, don't run away, just let it come to you. When you fly to the air from the tornado, you have time to shoot that Convexity beam at Gaul. (You know you can control the direction of the beam right?) Also when Gaul rests after shooting the eye-beam you have time to shoot him. Just keep doing this all the time. When you've beaten him comes the easiest part: do the dark fury.

PS: It's not Garr, it's Gaul.