Chapter 1: Legend of the Dark Mask.
In a certain dimension known as Mewni, there was a dark relic that was stowed away in that dimension's most fortified chasm, away from all life so it wouldn't bend the minds of mortals. The relic was a suit of armor, not a suit of knight's armor or a suit of armor of that of a samurai, but it was more of a single black mask that when worn will give the wearer a suit of powerful armor that grants them amazing abilities such as super strength, super speed and energy projection, all for the cost of slowly devolving ones mind into a rotten pile of matter that is addicted to wearing the mask.
They were many that used the mask before it was stashed away from society for good, some used it for good such as fighting monsters that threaten the lives of many and some used it for evil by slaying and killing others out of vengeance or in fits of unbridled fury, nevertheless, most if not all became addicted to wearing the mask to the point that they die if they do not wear the mask within three days.
The Mask was first discovered deep underground by miners of the Mewni kingdom, almost instinctively most of the miners agreed on to not present the mask to the king and queen of the land after one of them decided to wear the mask, the mask passed on from user to user becoming heroes of the people due to the immense power and strength the mask can give to the wearer, the mask became something of a well-known subject to talk about for the peasants of the kingdom whenever any authoritative figures aren't around, this is because they wanted something to believe in, they wanted something to hope for when their homes are nothing more than shacks and the food that they eat are nothing more than rot and mold with rat for good measure. They wanted a powerful figure that can shape the kingdom for the better and they believed the wearer of the mask could do something like that.
Of course, the wearer of the mask has free will so their moral compass is all over the place, some of them are actually that beacon of hope the low-born Mewnians need but lack the cleverness or knowledge on how to change the kingdom for the better, some use the mask to do evil rather than to repel evil, using their newly acquired power and exploiting it for what its worth.
After many users of the mask and after many escapades of the mask users, the many peasants formed a union and finally came to an agreement that the mask did more harm than good especially with results such as the many deaths of both Mewnians and monsters, and with that united agreement the miners were told to go back into the mines and place the mask to where it belonged right before closing the mine once more with a forced cave-in.
So when the miners did so, the mask became an urban legend to the low-class society of Mewni, but being completely unknown to anyone of royal and noble ascent, as the mask was stored back into its rocky and intrepid chasm, the mask simply waited for someone to waiver and destroy the mine due to the aggressive temptations of the mask, no one came when it waited thus breaking the cycle of someone finding the mask, wearing the mask then dying only for the mask to find a new mask bearer.
Of course this whole discovery of the mask was years ago, and with time, things change, positions of power changes, traditions change and even the location of the Mask changes, however what doesn't change with time is the desire for power, the desire to be strong, and the desire to obtain that strength. This is a story about someone who has those desires, after a certain series of unfortunate events, that'll eventually lead him to the mask. The Dark Relic that bestows the user with a blessing but in the end