All pets take the same amount of food to level up. From level 1 to level 10 you need a total of 10,220 Food. It’s maxed at 10 for a certain time. To level up further you need to expand your land (Expansion Lvl 4; Cost 2,000,000 Golds), and then fix the Black Tortoise Temple (1,000,000 Golds and 1 hour).
After fixing the temple you can level up your pets to level 15, but I suggest you to level up them when you find a certain enemy that you can’t defeat (on the Kung Fu Arena or League), because it takes a lot of food beyond level 10.
For Lvl 16 to Lvl 20, you need White Tiger Shrine (lvl 6 Expansion; 15.000.000 Gold) and then pay 2,000,000 Gold and wait for 15 hours to fix it.
There are 2 kind of levels. Normal Level, which leveled up by food. Battle Level which leveled up through battle and training. To train your pets you need a Gym. The amount of gyms which you can build depends on your level (at level 17 I can build 6 Gyms).
The price of Stg. 2 and 3 are upgrade cost (you can’t buy the 2nd stage or 3rd stage directly)
Sandbag Gym (available at level 8)
Your first gym, use it at the beginning and sell it after you get better gym, the exp ratio is the best, but unless you want to check your game every 5 minutes stay away from this one.
Log Gym (available at level 11)
You can train your pet from Lvl 1 to 5 (promote to Lvl 6) simply by using 1-hour training facility (Full upgrade).
Skyhigh Gym (available at level 17)
10 hours wait time
This is the best gym you can buy with golds. Keep at least one log gym because this gym generates too much exp for lvl 1 pet (the exp lost at lvl 5 promotion test).
Train your creature using the log gym (max upgrade), this will level up your creature to level 5 (promotion level). After finishing the test, train your creatures at Skyhigh gym, this will level up the pet to level 10. After this stage simply train your pets on skyhigh gym (count the training time, so it won’t stop training at the midnight when you already sleep).
When your pet reach certain battle level (5, 10, 15) you will need to do a promotion test. It’s very easy, just tap at the object at the right time. At Lvl 10 promotion test you have a chance to obtain a gem (even 2 gems). I believe you also get it at Lvl 16 promotion test.
First of all, the most important thing on the battle is element weakness. The pet’s weaknesses depend on the major element (the element that located on the leftside).
Example: Leaf deer, she has forest and earth element. Her left element is forest which means her weaknesses are fire and Ice.
|Forest||Fire and Ice|
|Earth||Plant and Air|
|Fire||Earth and Water|
|Ice||Fire and Dark|
|Lightning||Earth and Ice|
|Water||Plant and Lightning|
|Air||Water and Dark|
|Dark||Air and Lightning|
You can still defeat pets that has higher level than your pets if your battle level is quite high. I find that with 10 battle level you can defeat 2 or 3 higher level pets if your pet have the elemental advantages. This is why I suggest you to distribute your food evenly to all your pets, because lvl 13 pets (with high battle level) still can defeat those lvl 15 mini-me dragon on the Kung Fu League.
There is also an immunity element for each element, a pet that immune to the element only take 0 (no damage) or 1 damage.
Thanks to Treelia for the info