Priest of Discord

You buy the game. You install it. You make an account, log into the loading screen, pick a character and name it after your favorite sci-fi, fantasy, or anime character. Your name is rejected many times. Finally, you find some alternate version of it on your fourth try, and enter Norrath.

When you enter Norrath, you take a look around and get familiar with some of the movement controls. You played the tutorial (yes, EQ originally had a tutorial), but now you are in a city. When you check your inventory, you see a book called "The Tome of Order and Discord."

This book is unfairly enticing. When you read it, it plays a weird kind of reverse psychology by telling you to destroy it if you don't use it, but that only real power can be obtained by embracing Discord. It's a Neo pre-matrix-red-pill-or-blue-pill moment. It's only interesting if you do the risky thing.

Except in EverQuest. When you give the Priest of Discord this book, you are immediately flagged for PvP. Your name becomes red in color, and the entire world can see that you are, most of the time, fresh meat.

The special thing about this mechanic is that it provided a diegetic transition from PvE to PvP that was WAY ahead of it's time. The developers, as young and inexperienced as they were in a genre that had yet to be defined, worked really hard to make sure that their world felt immersive, even with something that most contemporary games would let a player switch on and off in a menu.