Instructions
Equip the Blango Fur Bow or a similar bow before you enter the area that Diablos is in. Equip the Hornet Armor along with the High Grade Earplugs to protect you from Diablos' high roar attack. Equip the Protection Jewel as well to protect against his Demonic Protection attack. Make sure you have the maximum amount of Potions, Steaks and Sonic Bombs in your inventory.
Eat Rations to increase your health and go to Area 7. Move to the giant rock in the middle of the area and you will encounter Diablos. Use a paintball as soon as you see him, then hide behind the rock. Draw your bow and shoot for the head. Use paintball again when he breaks from the trap and repeat this process until you break both of his horns.
Wait for Diablos to begin charging at you. When he does, move out of his direct path, then run at him at a 45-degree angle to get close enough for your attack. After the charge, he will attempt a horn thrust at you. When this happens, attack with the bow and aim at the left leg or tail.
Keep avoiding the charge attack and attacking with the bow when he attempts a thrust toward you. Ocassionally, Diablos will do a dig attack where he will burrow underground. Run in circular motions around the ground where he went in until he pops back up. When this happens, you have time to fire a shot or two from your bow.
Fire your bow when Diablos attempts his scream attack. It will not affect you if you have the proper armor and equipment listed in Step 1. Keep aiming for the left leg, tail and wings if they are open until you are victorious.