This supplement features 4 neat new monsters, and corresponding Aging Charts that alter said beasties with age--you know, adding Hit Dice, new Mutations, etc.
The charts are EXTREMELY thorough, as some provide chronologies broken down into hours and weeks of age, instead of just months and years. This process both expands the detail level beyond the "simplistic" OSR vibe of the monsters in the 'Mutant Future' core rules, and complicates things by adding a new layer of bookkeeping.
Personally, I like things stripped down, but I can see these charts being extremely useful for Mutant Lords who want to spice up their critters.
[3 of 5 Stars!]