[mivayan]

If it had such an impact as you to not summon it because the flavor text says it uses a dead mage to power the Behemoth, it just means to me that they did a very decent job of flavoring that particular unit.

Here is how I read the description: "bla bla reanimate dead elephant bla bla bla high magic resistance. As all of the mage's energies are used in controlling and preserving the beast, he or she is unable to cast spells".

This made me think that my mage would be unable to do anything usefull for as long as the behemoth lived, which seemed almost reasonable considering how impressive an undead elephant might be. It was not untill I read the description 10 times that I realized that a dead mage was reanimated as well to controll it, and that the reanimated mage was the one not casting spells.