Features:

1. Variety: Include a wide range of animals from different habitats - jungle, ocean, etc. This diversity will appeal to a broad audience.

2. Detailed Illustrations: Ensure that the coloring book features highly detailed and intricate illustrations of the animals. This will challenge and engage both kids and adults.

3. Spiral Binding: Opt for a spiral binding that allows the book to lay flat, making it easier to color and remove pages if desired.

4. Stickers: Add a section of animal-themed stickers at the end of the book. These stickers can be used to decorate the colored pages or for other creative purposes.

5. Tear-Out Sticker Sheets: For convenience, provide tear-out sticker sheets so that users can remove stickers easily without damaging the book.

6. Sustainability: Consider using eco-friendly materials and printing processes to align with environmental concerns.

7. Size: 25x14cm