Merlin was the ancient wizard from the Arthurian legends. He was Nox Decious' older brother and Mario's ancestor.
Originally, Merlin was called upon to find a Chosen One and when Decious discovered that the Chosen One wasn't himself, he turned to evil and viciously battled Merlin, who had scarred his brother's face in self-defense.
Afterwards, Merlin came to the Real World under the alias Nilrem to inform Mario and Luigi of Decious' plan to take over Earth and destroy everything good.
Merlin was a powerful and ancient wizard from a very long time ago.
King Arthur successfully killed the king and took the grail from him, only to destroy it. Later, Merlin was killed by Morgana so that nobody could stand in the way of her and her son Mordred who she gave birth to not long after she killed Merlin. Later on, Merlin was revived, only to again battle Nox Decious. A flashback of their final battle and the burning of Nox's face was revealed not long afterwards. Merlin either died and was resurrected once again or Decious thought he had died when he, in reality, had not.He and his brother Nox were supposed to help banish a great evil from this world. Merlin was called upon to find a Chosen One and originally thought that King Arthur was the Chosen One. This would make his brother be furious at him and, eventually, would lead to his brother entering Ganon's services. Eventually, Merlin confronted Decious, and while he was defeated, Merlin was able to destroy Decious' face before things could get worse. Later, Merlin sent Arthur on a quest to find the Holy Grail and defeat the Druids, along with his companions Sir Robin and Sir Lancelot.
After creating the Darkness, Decious targeted two infants of their lineage, whom Merlin was able to hide from his evil brother. After King Bowser had Kamek destroy the plane they were on, Merlin was able to save the two children and teleport them to Yoshi's Island, where a brave Yoshi brought the two to Merlin. Merlin gave them their hats and decided to raise them himself to combat the evil that was prophesized to come.
Mario and Merlin meet face to face and the wizard begins to answer many of the questions that Mario wished to know. He tells Mario he is one of the two Chosen Ones, but doesn't reveal that Wario is the other Chosen One. goes under the alias "Nilrem" and tells Wario how to re-activate the Nether Saber, even though he is unaware that it was him that de-activated the Nether Saber to distract him. As he was caught up with re-activating the Nether Saber, Waluigi was secretly being trained by Merlin to protect Wario. Eventually, when the Darkness confronts him, Merlin reveals his true identity.
Later, Merlin appears at his table after Mario's battle with Wario. Merlin tries to answer more questions from Mario. He warns the hero not to chase after the Darkness and that he will come to him soon enough.
In "Arc II Part 4," Mario confronts Merlin at his table, angry that he told him to wait for the Darkness, claiming it was the cause of Link's death. Merlin tells Mario that Link's death was unfortunate, but necessary. Mario doesn't see how, but Merlin tells Mario that everything is going to be all right. He tells Mario that all the events that happened
In "Act II Part 5," Merlin finds Waluigi at Merlin's table, telling him about their triumph over the Darkness because of the counter curse, which makes Darkness dead forever. Waluigi claims that he didn't give Wario the counter curse. Merlin gets angry at Waluigi and tells him that without the counter curse, the Darkness cannot be truly killed.in his and Luigi's life leads up to this. He then warns Mario about the Black Widow Blade and to be careful about the decisions he makes. Merlin then tells Mario to leave and Mario does.
Merlin confronts Wario and gives him 3 pieces of advice in the form of riddles. The first instructed him to stop the Energy Source from being destroyed, the second was that Waluigi was the key to getting their powers back and about the imminent threat of the Trifecta, and the third was a warning to Mario about his shadow. After explaining to Wario, Merlin bids him farewell and leaves without an explanation.
It is later revealed that after talking to Wario, the sorcerer left to stop Ganon from resurrecting Nox Decious, but arrived too late. After Decious revealed the villains' plan to invade the Real World, Ganon arrived, killing Merlin against Decious' wishes by choking him. It is suggested by Wario that Merlin isn't really dead, as the Nether Saber still works, though this is because the saber is bound to Merlin's immortal spirit.
When Mario, Brock, and Gary locate the Master Sword in the lost woods, they are unable to pull it out of its resting place. Mario then hears, to his disbelief, Merlin's voice in his head, telling him not to give up. Merlin then informs Mario that, if he had the sword, he wouldn't be strong enough spiritually to use it. To remedy this problem, he decides to train Mario in basic wizardry, in order to strengthen his mind and spirit. As their training progresses, Merlin is impressed by Mario's progress after only an hour. In their first battle, Nox Decious reveals to Mario that he killed Merlin in their fight. Mario refuses to believe it, but none of them are sure.
Later, he tells Mario that his training is complete and he can now pull the sword. However, it doesn't work and Merlin decides, along with the Darkness and Link, to transfer his spirit to Mario, giving him the wisdom, power, and courage that he needs to pull out the Sword. It succeeds, leaving Merlin's spirit forever inside Mario.