This is a new feature on the Big Update (25 June 2015)
Minimum Level Requirement : 15
Build time: 48 hours
Exp Given: 100,000
In the new update there are few pets which can’t be summoned. They can only be obtained using the soul stones. To get soul stones you need the Pond of Souls. The Stones are also needed to upgrade your habitat to 3rd stage and further.
In the Pond of Souls, you can exchange your pets to get the soul dust. You can convert soul dust into a soul stone.
No, you can’t.
you can only exchange certain pet that has element and level which requested on that period. Also, not all pets will give you same amount of dust. On the screen shot above, you don’t need to use Forest Lizard, any pet that has Forest element can be exchanged. The things which affect the amount of dust:
 Pet’s rarity, the rarer the higher the amount of dust that you will obtain. Example: Fruit Boar will give more dust than Leaf Deer since the fruit boar is more rare than leaf deer (assuming both of them have exact same level and battle level).
 Pet’s level and battle level, you will obtain more dust for higher level pet (of course). See the sample screenshot below to see what I meant.
The screen show you that lvl 10 flower frillzard generate more dust than lvl 1 (left and middle picture), the battle level also affect the dust as you can see that flower frillzard with higher battle level (right picture) generate more dust than the the lower one (middle picture).
Here are the steps to conquer the Pond of Souls every time,
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