Monstrilio is a hard novel for me to pin down. If I had to attach some labels to it I'd say literary fiction with a dash of horror.

It's a story rooted in loss: Magos and Joseph's son Santiago dies suddenly; Magos is enthralled by a tale about regrowing a child from its heart and so cuts out a piece of Santiago's lung from his body to do the same. As she feeds it and grows this lung, it becomes a monster that she treats as her son, and names Monstrilio. The book is divided into four parts from different perspectives: Magos, longtime friend Lena, Joseph, and finally Monstrilio.

But it's not just about grief, it's a story about family and relationships with the monstrous. Magos lives in denial and tries to believe her lung monster Monstrilio is her child Santiago again. Joseph speedruns acceptance and tries to forcibly conform his own life and Monstrilio into a facade of normality.

It's satisfying to me that the book ends from the fractured perspective of Monstrilio, rather than through the projecting biases of the adults in his life. It's interesting to see how the adults largely try to cover for Monstrilio's (at times horrible) actions and coerce him into humanity, while Monstrilio himself covers his own monstrous feelings from the adults and tries to exist in an ill-fitting human world.

I was quite engrossed by this book, although it is definitely quite (deliberately) uncomfortable at points and the book doesn't shy away from (usually off page) gore.