Re: Source of power for the Cthrag Yaska
The orb is very powerful.
For example, it cracked the continents in two, which seperated the greater body of the Angaraks from the Western countries.
It is basically the physical embodiment of "Destiny" as such.
This is explained in greater detail in Eddings "Mallorean" series, but there are two conflicting destinies at large in the world, each in the form of an orb (you get to see the "bad" orb - Cthrag Sardius - at the end of the "Seeress of Kell"). The whole plot of the Mallorean series is because these two destinies have to confront each other and resolve it so that only one of them continues.