This publication was offered on request from TSR and became part of later printings.
From the title page:
Welcome to an expanding universe! This is the official GAMMA WORLD rules supplement and presents new unpublished material as well as clarifications and corrections to the existing rules.
When we created the Third Edition GAMMA WORLD rules, there was a lot of material that we did not have room for and was therefore withheld. However, in our rush to get this new GAMMA WORLD game to you, we failed to delete many of the references to those sections.
We received an overwhelming response from you, our fans, congratulating us on the new game, but bemoaning the absence of these important sections. It is for this reason that we have created this official rules supplement and are making it available free to provide you with the most complete science fantasy system possible within the swiftest time.
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This supplement contains the following:
Complete errata to the third edition rules.
New Plant Mutations
New Robots
Cryptic Alliance details
Skills (Optional Rule)
Barter Rules
Price Lists
Equipment descriptions
Vehicles
Structural Hit Points
Typical Dangers & Hazards