The Diablo 2 Wiki
The Diablo 2 Wiki archive is available for anyone looking for information on Diablo 2. All information here is pre-D2R but contains a lot of useful information that is still relevant. Updated sections for new D2R features can be found on the PureDiablo Diablo 2 section

Monster Types

From Diablo 2 Wiki

This page lists all the types of monsters in the game, sorted by act. Each type is linked from the Monsters Category as well. Each monster has a page with information and stats; click the links to view those.

Act One