I was born in 1981, and when I was a kid around maybe 4-8 years old I had a book that I took with my everywhere. It wasn’t a novel or story, but a book with maybe a hundred different chapters (each chapter maybe 1-3 pages) of games/puzzles/poems/jokes/riddles/etc. Some of the specific items I remember were codes that you had to read by holding a mirror up to the page. I remember a page with funny looking monster heads. Pages with jokes, etc.
I had a hardcover book with maybe a couple hundred pages, that was outstanding. If my memory is correct the dimensions of this version were about 8 inches tall by 6 inches wide. My version had black and white pages, I don’t recall any color other than the cover. I do seem to recall that the cover has yellow as a prominent color in the design.
This my sound crazy, but I think having that book in my developmental years helped my brain in creating a high level of intelligence. I am about to have a son and would love to be able to give him the same book.
Could it be “Super-Colossal Book of Puzzles, Tricks, and Games” that was published in 1978? My copy was probably 8 x 10, but it had a yellow cover with monochromatic interior illustrations/headings. It had a page with a monster head (one of the party games), riddles, jokes, games, codes, calculator writing, etc. It sounds similar to what you’re describing. Good luck!
“A Treasury of Games, Riddles, Mystery Stunts, Tricks, etc.” by Carl Withers. There’s a copy on Amazon.