So I've had this idea for a while now, and I thought I'd share it. So my idea is, in Miitopia, when 2 Miis reach a certain relationship level (50 maybe), you are given the option to get them married (this only occurs after beating the Dark Lord. If you have gotten multiple to this level at one time, a random 2 Miis will be chosen and the relationship level will temporarily be leveled up to a random number for others). If you pick "No", the Miis will not get married (you can maybe change this later?), but if you pick "Yes", then you will be given the option as to which Mii proposes, unless one of them is the protagonist, who in which case will always be the one proposing. After selecting the Mii to propose, the Mii will say yes (the reaction depends on the Mii's personality). They will next be seen in a church, and you will choose a Mii to play the Vicar. After the role is decided, the Vicar does the honours of marrying the Mii couple, as the crowd (made up of team members, characters encountered across the story so far such as the Dubious Mayor, the Worried Mother and her Child, the Desert Celebrity, the 3 Fab Fairies fans, the royal court, the genie and the Fab Fairies, along with random other Miis (mainly placeholders for teammates at the villa after the story is over). But before the ceremony can be completed, the 2nd Mii (the one who was proposed to) gets their face stolen! The 1st Mii and the others wonder where they went, before the vicar spots something floating above - the White Demon, with the 2nd Mii's face on! The White Demon is a white creature with a round head and a white cloak, similar to the Darker Lord. He says "Finally, a face! Ha ha! It's been a hard journey from New Lumos, but it was worth it! Ha ha!" The protagonist asks "Who are you! Give back [2nd Mii]'s face!" and the White Demon says "Oh, hello! I am the White Demon! I was created by the Darker Lord, but deemed too similar in power to him, so was cast away to live in his city of nightmares, with no face. But I escaped, and have found a powerful face, so I can get my revenge on the Darker Lord! But I will need servants, so I have come to the right place!" He extends his fingers, and steals the faces of (either the king, the princess or the genie), one of the Fab Fairies, 2 of the townspeople (possibly all 3 of the Fab Fairies fans at once), the vicar, and 2 of the teammates! He holds the faces in front of him, and says "This should be enough for now. I will now go to look for the Darker Lord. You shall not follow me, as if you do, you will be pummeled to death by my servants! Just stay, and watch your friends cower in despair!" He vanishes in a flash of light, along with the faces. The 1st Mii looks shocked and devastated, but the guardian spirit speaks to the remaining members, saying "Ho ho ho! It seems you have got yourself in quite the pickle again! The White Demon, eh? He's one of the strongest of the Darker Lord's creations, and now has taken the faces of these people, and your [Bride/Groom]! Well no need just sitting out here mourning! I've seen what you can do! Go out there and give that Wedding Crasher a good beating, and save all the poor souls he's taken, including your [2nd Mii]!" The guardian spirit's words make the remaining team determined to save their friends, and they go and hop on Dominic to rescue them. The faces are in random locations across and around Miitopia (no matter how much you've unlocked, although you can never find yourself in the Sky Scraper, Otherworld, or New Lumos). A red exclamation point points to where the White Demon is, and you cannot do Travellers Hub quests during this period. Every time before a boss fight, the White Demon appears and expresses surprise at seeing the team, before saying that he has still not found the Darker Lord, and will look elsewhere, leaving a monster to "finish off" the team, before disappearing. After defeating the boss and rescuing the stolen face, a red exclamation mark points to another location in Miitopia, where the same events happen, only with different monsters and the White Demon expressing more surprise every time he sees the team. After defeating 5 bosses in 5 different worlds, the White Demon appears and says that he is sick of seeing them alive and well once again, and says that he "knows for sure" where the Darker Lord is hiding, and tells the team "catch me if you can!" and leaves the final "teammate" boss for the team to fight. After the team defeat the boss, the guardian spirit tells the team of a hidden realm, that's gate only unlocks every time 2 Miis get married. This realm is revealed on the map to be in front of Miitopia, looking heavenly. The team hop on Dominic and fly to the hidden realm. In this realm are only three stages. The first one contains normal enemies, and the second one also contains normal enemies before a boss at the end - A red demon with the face of the Vicar, accompanied by two Fiends. After defeating the "Vicar" Demon, the stage ends, and the player advances to where the White Demon lurks. When confronting him, he says that he has not managed to find the Darker Lord yet, but might as well get the team out of the way by himself. A voice then comes from behind them. It is revealed to be a green Imp with a blue cloak, a member of the "Imp Patrol", and has come to defeat the White Demon, and will be glad of their help, despite being enemies. The battle with the White Demon commences, with help from the Imp Patroller. After beating him, he disappears, and the 2nd Mii is freed. As the Imp Patroller is celebrating the victory, he remembers to kill the teammates, before finding that they have disappeared. Their marriage commences, and all the Miis celebrate, with the Roving Photographer coming and taking a photo of them all, most prominently the new married couple.
When the White Demon appears in the church when this event occurs after the first time, the cutscene will occur differently to how it occurred the first time. The White Lord will not explain who he is again, presuming that the Miis already knows who he is. If the player has completed the main game, the guardian spirit will make a reference to the Darker Lord being dead.
If two or more of the players are level 30 when fighting the "Vicar" Demon, the Fiends fighting alongside it will be changed to Terror Fiends.
The "Imp Patroller" also appears as an enemy in the Sky Scraper and New Lumos.
If the player has completed the main game, one of the team members will tell the White Demon that the Darker Lord is dead when confronting him for the last time. This is what causes the White Demon to fight the team this time around, instead of just wanting to "get them out of the way".
The White Demon has the "face steal" ability that the Dark Lord has, meaning call Imps and put the faces of current teammates on them. However, if the player has completed the main game, he will put the faces on Fiends instead of normal Imps, making the battle a lot harder. This is presumably due to his rage at the team having defeated the Darker Lord, keeping him from getting his revenge.
Another rare occurrence that happens after beating the game, is the White Demon transforming into the "White Sun" (like the Dark Sun and the Darkest Lord), making the fight harder, and also changing the Music. He can also steal the faces of current teammates and put them on coins, just like the Dark Lord can. Despite this, he is still less powerful than the Dark Sun.
It is never explained how the White Demon keeps re-appearing, and (after completing the game) forgetting that the Darker Lord is dead every time (even though he technically isn't, which also isn't explained).