This is the prologue of Paper Mario: The Mystical Artifacts.
Prologue: Return Of The Skull King[]
-Mario's House
The game begins when Mario receives a letter from his friend Merlon, who has something important to tell Mario and wants him to come over to his house. Mario then tells Luigi that he's going to Merlon's house and leaves. Just before leaving, though, Mario picks up his hammer, feeling that he may have to go on an adventure again.
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-Toad Town
At Merlon's house, the old and wise Shaman tells Mario about what's going on: ages ago, an evil and powerful demon known as the Skull King tried to destroy the universe. Many villages were destroyed by the king and his army, but fortunately, a brave warrior defeated the Skull King before he could cause any more destruction. This warrior was helped by five powerful treasures known as the "Mystical Artifacts", which were created by the "Light Shaman", also known as Merlinius.
However, just as the warrior was about to deliver the final blow, the Skull King escaped the battle, never to be seen again...until now, that is. Recently, Merlon discovered that the Skull King is back and still plans to destroy everything. Even worse, the fiend found out about these powerful objects known as Dark Pearls, which contain a high amount of dark energy, and he sent his minons to collect as many of them as possible so that he can absorb their powers and become powerful enough to destroy the whole universe with ease.
So, basically, here's what Merlon wants Mario to do: collect the five Mystical Artifacts, which have been scattered all over the Mushroom Kingdom, and defeat the Skull King before his minions collect enough Dark Pearls. Of course, Mario can't refuse, as there's no one else who can accomplish this task, so he tells Merlon that he will do it. Merlon thanks Mario and says that he should go to Gloop Gloop Lake, where the first Mystical Artifact, the Ancient Bracelet, is located. Merlon then says that Mario can get there from the Mushroom Fields (the main hub of the game), which is just outside of Toad Town. Mario thanks Merlon for the information and leaves his house.
Just then, a Toad shows up and tells Mario that Princess Peach wants him to come over to the castle. So, before leaving town, Mario decides to go to Peach's Castle.
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-Peach's Castle
There, Peach tells Mario that she heard that he was going on an adventure, so she decided that he should have a few supplies. She then gives Mario a few Mushrooms, coins and a badge (which she then tells him how to use). Mario thanks the princess and leaves the castle.
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-Toad Town
Just as Mario's about to leave Toad Town, he meets a young Brock girl named Bianca, who is a big fan of Mario and adventurers in general. She tells him that she recently heard about his adventure, and wants to know if she can join him. Seeing that she won't take 'no' for an answer, Mario decides to let Bianca join him. With this, the duo leave Toad Town.
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-Mushroom Fields
Mario and his new partner head for Gloop Gloop Lake, though they are soon attacked by a Goomba, a Para-Goomba and a Spiky Goomba. During the battle, Bianca gives Mario a few tips about battles. After defeating the Goombas, the duo finally reach their first destination, Gloop Gloop Lake.
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Meanwhile...
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-Skull King's Palace
The Skull King is told by one of his minions, a Dry Bones, that "some guy named Mario" is after the Mystical Artifacts. The Skull King says that, even if "this nobody" manages to collect all artifacts, he won't be able to defeat him when he absorbs the powers of the Dark Pearls.
"And soon, this universe, along with this pathetic fool, will be no more! Gwah ha ha ha ha!!!"
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End Of Prologue.