The Book of Spells just came out, and some of it's pages is written in “low Mewnian”. So here is official decoded Low Mewman alphabet (posted by Gravityfying) so you ca translate pages by yourself or enjoy using this to hide your inner sorrows.
Here are pages written in “low Mewnian” in Eclipsa’s chapter.
Note that the numbers are a notation of time for the events. Eclipsa doesn’t specify what it means, but looking at the other chapters it’s most likely “Day XXX in the Era of the Spade”
The Prince Of Darkness [Globgor] was right about the Septarians, their army is growing and they are even recruiting other monsters outside their own to join them. There’s really too much to explain here but I’ve developed an extreme option, something that may prove useful against the Septarians.
Due to the severity of the consequences of this spell, I refuse to give it a name. It should never be used unless it must be used. For this spell to work, you must aim your wand directly at your adversary’s heart, then recite this poem:
“I call the darkness onto me, from deepest depths of wind and sea. From ancient evils unawoken, break the one that can’t be broken. To blackest night I pledge my soul, and crush my heart to burning coal, to summon forth a deadly power, to see my hated foe devoured.“
If you are wondering, I have witnessed firsthand the results of this spell. I’ve used it and it works against the Septarians. I’ll say nothing more about it.
Tonight I make my escape. To the future queens who inherit this book: I hope that time will show my decisions were just and right. I don’t know what the future holds for this kingdom, but it’s clear the mounting tensions between the monsters and Mewnians are at their peak. I know it seems like I am thinking only of myself in this decision, but maybe it benefits the kingdom too.