r18586 adds a stab at familiar data.
Some look safe:
Unspeakachu is a physical starfish
Stooper gives +1 liver
Disgeist is probably just a reverse Hound Dog (-15% combat and 3 lbs gave 7 'and ons' in Airship, 13 and 23 lbs gave 8 'and ons', 98 lb gave 9 'and ons'.
Bowlet is physical damage and items, haven't spaded items, so assuming fairy.
Cornbeefadon is stats and meat, haven't spaded, so assuming volley and lep.
Mu is elemental combat, all types, every round! New go to familiar for maximizing damage sources?
What else are we missing?