I remember King's Quest 3 had a bunch of spells and/or potions you needed to use to win the game that required precisely worded commands, and they were only included in the physical manual.
KQ6, in addition to being one of the greatest adventure games of all time, had some of the best copy protection.
The manual had an extensive "encyclopedic" section that was part background material, part hint book, and part ingenious copy protection. For example it included the following 'poem' as background material about one of the game areas:
Three roses laid upon the bower,
A scythe for he who cuts the flower,
A crown, a dove, most noble race!
Thy bones make sacred this dread place.
As it turns out, this poem is really a solution to a puzzle where you must walk on the floor tiles in a particular order to survive:
There were several solutions that were cryptically hidden in the manual like this, such that people who hadn't read it would get stuck at various points.
The real genius however was that this was before the Internet, and so if you wanted hints you had to call Sierra on their special 900 (toll) number to get help.
I remember this as well! There were also some incomprehensible glyphs on the tower climb, leading up to the Winged One's(just prior to the Catacombs in your screenshot) that were only printed in the manual.
Metal Gear Solid for the PS1 had something similar - it referenced a radio frequency on the back of the CD case, so if you copied the game but didn't copy the liner, you'd end up getting stuck.
What a joy to play that game. One of the first games (I'd played) to take on a cinematic feel all in-engine.
Regarding KQ3, I miss those little hint books you could buy for the game that came with the red reading window. Totally not necessary today, but it was a fun thing to have back then.
I had a printout of the spell book, and there was a typo in it. Since it was an uncommon word, I didn't catch it, and didn't think to look it up. In class, we encountered "soporific", and I thought, "oops, I guess 'soponific' isn't right..."
A number of the Infocom games required the use of various objects/information included in the game box such as decoder wheels. Wouldn't be effective today of course but it worked pretty well pre-Web when you didn't have easy ways to trade this sort of information.
The manual had an extensive "encyclopedic" section that was part background material, part hint book, and part ingenious copy protection. For example it included the following 'poem' as background material about one of the game areas:
As it turns out, this poem is really a solution to a puzzle where you must walk on the floor tiles in a particular order to survive:http://i.ytimg.com/vi/WUw771rvxhc/hqdefault.jpg
There were several solutions that were cryptically hidden in the manual like this, such that people who hadn't read it would get stuck at various points.
The real genius however was that this was before the Internet, and so if you wanted hints you had to call Sierra on their special 900 (toll) number to get help.