The Shadow of Yserbius, originally published by Sierra On-Line and developed by Joe Ybarra of Ybarra Productions, was the first of three graphical MUDs for the online community. Opening to rave reviews, The Shadow of Yserbius, according to industry critics,[who?] set the standard by which all future MUDs would be judged. The game was followed by two sequels entitled The Fates of Twinion (1993) and The Ruins of Cawdor (1995). Until recently, only The Shadow of Yserbius and The Fates of Twinion were playable in offline mode.

The Shadow of Yserbius, along with its successors, remained online until 1996, when America Online purchased the rights from then-owner AT&T for an undisclosed price (rumored to be $40 million). AOL soon pulled the plug on The Shadow of Yserbius, which was a competitor to its existing online RPG Neverwinter Nights.

In late 2007, the ImagiNation Revival Project succeeded in resurrecting the long-dormant ImagiNation Network by using the original client software coupled with DOSBox. The Shadow of Yserbius was again available for online play with all features, graphics, sounds, and such fully intact and functional. Macros are fully supported and compatibility with old character and map files is enabled for TSN/INN versions 2.4 and higher. In early 2016, the server was shut down making online play not possible.