Full color picture book. A boys parents warn him not to go into woods. He sneaks out anyway, each page is a separate part of the woods and he encounters a unique type of creature/monster per page. I think one is like a colony of tree people, but at the end of the woods and in the final pages he starts getting chased by a smog creature, for like 4 pages he’s just running as the color pages are filling up with smoke. He barely escaped the forest and gets back into house or bed and thinks to himself “never doing that again”. The big part of the book is the escaping through the forest and running home from the smoke (which looks similar to a dragon maybe) but I think they never reveal what the monster is. This book is probably 14-33 pages. The other identifier is that each stage of the forest is a unique creature. Fantasy vibes. Pretty sure the book as color as well. – I know it’s not where are the wild things, and I know it’s not the tomtins.