When you reach the underground Castle area in which you have to fight two El Gigantes, you can bypass this difficult fight entirely. Climb the ladder and ride the zip line down to the trap door switch. Run back and do this over and over again really fast. Eventually you'll be able to get to the zip line before the actual zip line does, and riding it down will trap you inside the wall. From there, turn right and walk through the wall past the locked door. This bypasses the fight entirely, because you're glitch-walking behind the spot where the cutscene for the fight is supposed to take place.