The stats were normalized around typical stats for pets. Not all pets actually have the same stats though they are nearly identical.

The normalization was done in a spreadsheet using a custom weighting that you can see here: http://i.imgur.com/B8xS4Nk.png

The "special field" marks inherit advantages or disadvantages in the base pet. For exmaple, flying creatures get a +1. I just made up the value of the field to take into account some things that are harder to quantify.

The original pet's "score" ranged from about 4-8 .. so a spread of about 2 to 1. I kept that spread, and kept the averages for the values around the same.

various changes:

• Small creatures have a lower reach multiplier.
  
• Apex predators like the big cat and the bear now do more damage.
  
• All furry creatures are less immune to fire.
  
• Bigger creatures and furrier creatures tend to stand up to ice better.
  
• Bigger creatures stand up to electricity better.
  
• Some creatures now move significantly faster (to match nature).
  
• Many creatures are now not quite as likely to help out when they see damage.
  
  Bat
  You might find an unmodified one of these in another mod or fish. I chose the Pets mod version, but then modified it like the others. This pet now also has a fairly small poison attack.
  
  Burrower
  You might find an unmodified one of these in another mod or fish.