[Welcome to the EL Book Introductions series. These posts are all short (<180 words) introductions/reviews of books in the EL library. They focus on telling you what we think will be interesting for you, a college student and English learner, so use them to help you find the right book for you. You can also use the tags to find books about topics you might be interested in.]
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You can guess from the title of My Big Fat Zombie Goldfish that this is not a very serious book. It is a very silly book meant for elementary school-aged children to read—especially children who have older brothers or sisters. It is about a boy and his older brother, who is an evil scientist. The brother is a bully, and does a science experiment on a goldfish. When the boy tries to bring it back to life, it becomes a zombie that can hypnotize humans. It is a silly, silly book.
Because this is a book meant for children, the author repeats a lot of words and phrases. This is a good way to learn a language. Also, many of the pictures in the book are visual puns (おやじギャグ), so even just looking at them can be English practice. Finally, there are some puzzles and an interview with the author at the end of the book. These can all be interesting even without reading the whole story.
My two cents: This book was first published in 2013, and I find it interesting to compare with Aliens Ate my Homework, which was written 20 years earlier. While the target readers and general themes are the same, the type of writing, humor, and general feeling of the books are quite different.