I don't think this can be found in the bazaar. Most, if not all, Polymorphs are non-tradable. This is the same for the Azteca Sun School and Star School treasure cards.
The polymorph treant spell is sold by a secret vendor in storm riven You know where koralak night spinner is? Somewhere behind that Building is a guy who gives 4 polymorph spells: Polymorph treant, lvl 55 Polymorph colossus, lvl 56 Polymorphelemental, lvl 57 Polymorphelemental, lvl 58
well I am sure by now you tried the bazaar and you can not get the spell at your level right? well here is the best way to get it at a low level. Trust me, I have about a hundred polymorph cards with my level fifteen fire wizard. yes I am only level fifteen and I have polymorph cards.
The trick is to garden, And have access to crowns. And you have to put the time in. If you follow these instructions, You will be a high level gardener in under a week. even in your dorm room you can reach level ten in gardening.
First you have to plant about twelve to fifteen key limes. You will have to get the medium size pots from the gardener in golem court. Then put one or two Garden Gnomes near them. If possible, put a water mole statue to. this all helps them grow quick. when you harvest all you key limes for the first time, you should be about seventh level in gardening. when you harvest them at elder, you should be tenth level in gardening. If you are level fifteen, Your first castle should be the red barn farm. If you are not level fifteen. then you can still do this in your dorm room. But it might take a few days extra. At this point, you have nothing planted since you are done with your key limes. Your nest move is to plant Red Grapes of Wrath about six to eight of them. If possible, put next to it a weapons rack. plant a Fickle pickle also. This all helps the grapes grow quicker. And smaller harvest times. Be sure to remove the Garden Gnomes, the grapes hate them. Now you have a good chance of getting polymorph treant as a drop from the elder stage of red grapes of wrath. good luck.
PS. moon flowers give all polymorph cards, You can get them from the ravens hoard pack.
Mark Dragonleaf L58 Storm Mark Shadowleaf L15 Fire Mark Dawndust L57 Balance
treant, lvl 55
colossus, lvl 56
elemental, lvl 57
elemental, lvl 58