What are the main differences between Diablo II Multiplayer and Single Player?
There aren’t a lot of differences. The characters, skills, quests, monsters, and all other basic game features are identical. Unlike in Diablo I, there are no single player characters in Diablo II; the characters and the game are the same, and single player characters in D2 are more accurately described as “offline” or “non-realm” characters. They’re just like characters on the realms, except they’re stored on your computer, rather than the Battle.net realms. Single Player characters can be played with other players, via TCP/IP or DCC or Open Battle.net The biggest difference for Single Player D2 is the addition of the players x command in v1.09, which allows solo players to simulate larger games. This provides a greater challenge and more items. Some items can only be found on the realms, not in SP (or non-ladder online play).
