And lo, the magic of the Jeshatan was twisted and strange. It bent according to their unholy desires; and they corrupted many before they had had their fill and walked away. But none could oppose their might; and so it was that the land was cursed by their presence and thus blessed when they left.
-From the 170,000 Scrolls of Bitterbark the Mad
The Jeshatan are a society of magic. Their dimension interconnects with dozens, indeed by some accounts hundreds, of different worlds. As such, their selection of spells might be considered unlimited. However, there are certain schools which have aided them considerably in their subjugation and control of the dimension. Specifically, the four schools of the Infernal, Knowledge, Accountant and Disease have had a very decided effect. Each of these four schools has a greater reputation among their number, and a specialist in each will quite often devote his entire focus of being towards mastery of them.