Instructions
Travel to Area 4 of the Flooded Forest and accept the Save Our Boat quest. A short cut scene will play showing the Royal Ludroth.
Attack the Royal Ludroth using your character's various attack abilities. The vulnerable spots to attack are the monster's head and spongy mane, as well as the torso and tail.
Focus your attacks on the Royal Ludroth's tail at the beginning of the battle. After you cause enough damage to the tail, it will fall off, which lessens the damage done by its tail attacks. The Royal Ludroth will still try to swipe at you with its tail, though a removed tail will cause very little damage.
Continue attacking the Royal Ludroth's spongy mane. You will see wounds appear once you've caused some damage.
Avoid the Royal Ludroth's roll attacks. Watch for this attack when he lifts his head and one front leg, then shakes his mane to the side. The best spot to stand during this attack is behind him.
Roll to the side when the Royal Ludroth performs a body slam attack. He will lift up on his hind legs just prior to doing this attack, giving you the opportunity to roll out of the way.
Follow the Royal Ludroth underwater once his health is low. Do not stay in front of him while fighting him underwater, because he has an attack that propels his body toward you.
Go to Area 8 of the Flooded Forest once the Royal Ludroth retreats there when close to death. Reach the area by going to Area 1 on the map and dropping down near the sleeping Royal Ludroth in Area 8. If he reaches the water, follow him in and finish him off.