So I'm gradually learning more about the pets and how they influence your wiz in battle. For me it's all about battle so please forgive me if I limit my comments to the battle aspect of pets and not the derby.
As your pet grows through the four stages:
At each of these 4 stages it appears that your pet learns a helpful action or attribute. See Patchnotes for more information.
As your pet grows in statistics it will reflect it's new found abilities on your character while in battle.
Strength = more damage, greater power pip chance, resistance
Intellect = more mana, accuracy, power pip chance
Agility = heath, accuracy, resistance
Will = health, mana
Power = all of the above
Now the following graphic from the Patchnotes holds the key to the mystery of HOW pets actually physically help (IF they do help).
As you can see a pet can potentially give you blades, disarm, or put weakness on opponents and I've heard that some will cast spells eventually if they are grown enough.
Other pets obviously will only give you additional stats, such as more shielding, power pips or a card etc. (like my colossus).
It seems that these talents and powers are uncovered typically one talent per level of your pets "age". For those that don't have a pet to the epic level yet and are sad that your pet doesn't cast anything... you can hold out some hope.
To me the ideal pet would be a school pet with school boost stats mixed with another pet that gives blades or debuffs. I think that pet could be an ideal helper.
Keep working on leveling your pets to uncover their talents. Let me know what your pets do as you get them leveled. Perhaps we can make a list of traits and see what pets are best to mix with.
Here's another code for the fastest wizard: It will work only for the first one to redeem it!