Quest for Glory Anthology Cheats

On the title screen, right-click on the scorpion crawling across the screen and you will get a message saying "Congratulations! You found the first bug in this game!"

The second time you visit the Mirror Lake location. Wait around a while and you'll see a periscope appearing in the lake, and a nonsensical message will pop up if you look at it. This is a reference to another Sierra adventure game, Codename Iceman, which centers around a submarine.