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

Category:Guest Monsters

Category page
Diablo II Monsters [e]
Types
AnimalsDemonsUndead
Info
Complete Monster Listing
ModifiersExperience
ChampionsSuperUniques
Monster Categories
AnimalsDemonsUndead
Act BossesGuest Monsters
ObjectsSuperUniques
Uber Monsters

Guest Monsters are special, extra-tough versions of monsters found only in Act Five on Nightmare and Hell difficulties. Guest Monsters were introduced into Diablo II in v1.10, breaking up the fixed monster spawn non-variety found in Act Five in the original version of D2X.