What do I do to make sure my pet gets 15% wards instead of 14% wards by the time it's mega? Do I feed it a specific snack? What is the category that should not be maxed, will, or strength, or intellect, or agility or power?
In order for a pet to ascertain it's maximum potential the fresh number for resists as you mentioned or even critical (critical striker etc.) or damage (pain-giver etc.), that particular pet will have to have their Base Stats very close to 250 as possible.
Those stats being Strength, Agility and Power.
If this is successful, then your pet will be able to as I'd put it, reach it's maximum potential and grasp the 10% of Spell Proof.
Another way to look at it is if all of the stats I just mentioned are about 235 or even higher, then this too will result in a pet maximizing it's full potential. That is, 10% Spell Proof.
I have however found that, if one of the talent, example, Power is at 250, and Agility is at say, 230, the pet still reaches 10%.
Bearing this is mind, you will be able to note if a pet will be able to attain this before even training it.
So, as the base number of these talents decrease, then, so will the % of spell proof.
Most cases, if a pet caps out at 4% defy, then proof is usually at a maximum of 8%, rarely does it attain 9%.
What do I do to make sure my pet gets 15% wards instead of 14% wards by the time it's mega? Do I feed it a specific snack? What is the category that should not be maxed, will, or strength, or intellect, or agility or power?
Strength and/or Agility should help increase your pet's resistance talent.
When looking at your pet in the Pet section of your book you can hoover your cursor over each category and see what it improves:
Strength affects damage, pip chance, resistances, outgoing healing, armor piercing, stun resistance, and the cost to cheer while swimming in the pet derby.
Intellect affects mana, accuracy, pip chance, incoming healing, armor piercing, critical block rating, and the cost to cheer while running on clay in the pet derby.
Agility affects health, accuracy, resistances, incoming health, critical rating, and the cost to cheer while running on grass in the pet derby.
Will affects health, mana, damage, outgoing healing, critical rating, critical block rating, and the cost to cheer while running on dirt in the pet derby.
Power affects most statistics and determines your pet's maximum Morale for the Pet Derby
In short, your pet should have Strength, Agility and Power as close to 250 as you can possibly get. If you can't get there by hatching, sometimes a "selfish talent" in the talent pool or added as a gem can help you make up the difference.