Ultima IV introduces the Virtues. In this game, the player must earn the title of Avatar by recovering the Codex of Ultimate Wisdom.
Not a hell of a lot of cheats or easter eggs in Ultima IV. You can try using the Skull of Mondain or casting spells you'll never really need to. One thing I noticed on the Ultima Collection version of Ultima IV, you can go to the places in the wilderness to find nightshade or mandrake root, get it the double new moons, save your game and when you reload the game will have reset so the moons are once again double new and you can get more nightshade or mandrake. You can do this as many times as you want, but it gets tedious and you won't ever need that much nightshade or mandrake.
Shrine mantras: