For those who haven't looked at Gamma World in a while, here's what its second edition rulebook (which was current at the time this article was written) has to say about new body parts:
Character has extra appendage or organ not usually found in his species. Examples include: A third eye in the back of his head, light sensitive antennae, arms and hands (for a fish or other species that normally doesn't have limbs), a head or brain for a Plant. The players always design the new parts, but the GM must approve the design.Now, I appreciate the brevity of this entry and its reference to the GM as the final authority in determining what is an acceptable new body part. However, as Maxstadt notes at the start of his article, "Some players have trouble inventing original mutations which are more than mere variations of the official mutations in the book." Likewise, there's always a tug of war between player and referee in trying to decide just what sort of mutation is "too much."
Back in '85, I'd neither developed a keen enough sense of "balance" to make such decisions with any reliability nor the dispassion I now possess about such concerns. So, when Maxstadt offered up a percentile table containing approximately 40 examples of new body parts, I was glad to see it. My players and I both found it easier -- and less stressful -- to roll on the table and be done with it. Nowadays, I probably wouldn't use such a table, but that's not an indictment of Maxtstadt's offering, which, like nearly everything he wrote for Dragon, was excellent. Rather, it's a testament to how much I've changed as a referee since I was a teenager -- something I hope is true of all of us who are still gaming decades later.