Interlopers from the Blasted Realm: A Creature Compendium is Volume 5 in the E.N. Critters line of geographically-themed PDF bestiaries. The document starts with a table of contents, then an overview of the eponymous plane, including two maps, and descriptions of the plane including various locales, local history, and the general ecology and culture. This is followed by stat blocks and descriptions of the demonic-themed monsters; tables sorting the monsters by CR (1–22), type, author, and artist; and 4 pages of two-sided counters.

Interlopers is the only E.N. Critters Volume with a "Warning: Gore Advisory" on the cover. With the exception of logos and product names, the monsters and the information about the plane is all Open Game Content, released under the OGL version 1.0a.

From the back cover:

Featuring:

• More than twenty all new demons and demonic creatures native to the Blasted Realm, a pocket plane of chaos and evil
  
• Charcoal and blood red illustrations throughout
  
• Detailed ecologies and background
  
• A Suggested Knowledge Table for each creature
  
• A Rules and Game Balance section for each entry
  
• Counters for all creatures
  
• Fully linked Table of Contents in the PDF version