For better or for worse, this was on the list of games I wanted to review. The why of that is the part that may annoy you or make you happy, depending on your goals. That cover image hit me and I was expecting this to be a somewhat whimsical silly game. I half expected it to be written in rhymes. Why? Because the combination of simple imagery, strong color distinction, and that font with the little person symbolically above it made me absolutely reliving my childhood. It feels like a full commitment to the Dr. Seuss evocation. I'll be judging the document on its own merits, but realizing it was designed to be horror enough to need a content warning was a slight disappointment. There goes my hopes of a monster stat block for a Lorax. Oh well.
I'm not familiar with the system in use here, so that's a point against me on offering useful insights on mechanics. Still, I am sure things will make sense enough once I dig in further. As I've said in other reviews, I am never a fan of more than a short paragraph of 'read-aloud' blocks. My style of running games doesn't fit with monologues well. I much prefer when these sorts of blocks include either a key point list at the end or bold words for key elements within the block of information to call my eye to what's going to matter on the fly. It allows those who like the read-aloud elements to have them while still allowing those like myself to have our own method addressed.
GM only section immediately references seventh son of the seventh son, evoking elements of Orson Scott Card's Seventh Son, and The Spook's Apprentice by Joseph Delaney. No idea if that was coincidence or intentional though. Especially given the similarity between Alvin and Alair. Weird little tale of what is going on. Missing a comma in the sentence about Yena though. Not a point issue, just pointing that out.
Not sure if moments are part of the system, but seem fine. Little tone aspects. At this point in reading, I don't see them more as bits of set dressing, but perhaps they come into play later. Treasures are alright. Two of the three are quite fun if the players decide to do something with them. Once I get down to the summer residence, I find a person who is hiding and knows what happened. When I look back at the GM info again to be sure I wasn't misremembering, it indeed says all of the people on the estate are there mesmerized. Perhaps change 'all' to 'most' in that case. Or 'nearly all' perhaps?
The mime enemies are,.. okay. Less than obvious weakness is fine considering it is caused by unholy beings. The list of 6 things they do feels a bit weak though. You are going to get a little unexpected backstory out of me here. In high school, despite being involved in athletics, I was also involved heavily in theater. One of the special clubs I was in was mime. Shocking they even had it as a club honestly. I spent 2 years studying mime and perfecting elements. There's a lot you can do with mime.
The most obvious option for combat is allowing some of the mimed objects and effects to become real. That's pretty bog standard though. What you can really make good use of is a little known element of mime. The line of silence (or circle of silence, etc). I'm not sure how much it gets talked about even in books and documentaries about mime. Basically, you may notice on almost every form of mime makeup, there's a very strong division point between the makeup and the skin. Sometimes it is just a crisp edge, other times it is marked with a black outline around the white. This is the silence line. For as long as it remains unbroken, the mime is supposed to stay silent. It's treated by some mime groups as a sort of sacred and unwavering barrier. To the point where the mime troop may banish you for breaking it and you need to smudge the line at the end of a performance before you can start talking again.
While it's a silly tradition I doubt most groups even follow, it is useful. It's a distinctive cut off between the real world and the performance. I could easily see you using this in your own setup here as a way to free the brothers. Smudge the line. Breaking the line frees them from the demon possession. Perhaps even allowing the demonic beings into our own world instead of inside the brother! Harder enemy in exchange for maybe saving a brother. Food for thought.
So then onto the last page I see an audience member wanting to escape. This strikes me oddly. Since the audience is captivated, this person has to be Yena right? But if it's Yena, I have a hard time imagining she's counted as a trap. Is the automaton going to be clawing her way out or something to cause trouble for players. It feels a little unclear here, at least for me how this person is still able to try escaping. The very next entry says Yena's there, so it obviously isn't her then. All quite confusing for understanding why there's now a second person not captivated in an adventure where 'everyone' is captivated and never leaves.
The slime's weakness is beautifully strange and entirely fitting. Without really knowing the system, no idea how well designed the enemies are for this, but they seem consistent in design. The ending itself implies there's no saving the brothers and they might recur as an enemy in the future. You gave a few options for player actions at the end, so it's not a railroad event exactly. I just really like the idea of a possibility of undoing the deal that transformed the brothers. Doubt most players would figure it out, but still noteworthy.
So overall, seems like it could be fun. There's a lot of silly turned horror possible. Lord knows there's a lot of sources for ideas from things. Killer Klowns comes to mind. The layout is clean and everything felt easy enough to find. It was consistent, but felt a little short. That's not an insult though. Wanting to see more and have a better feel for the setting, world, and adventure are a good thing. Nicely done on this overall.