I have Dragon Fear on Tywin Lannister, Core Set and the The Power of Blood is revealed.
I win a Military challenge against that player. Can he choose to have Tywin be "killed" for claim if he can't be killed or must he chose a character that can actually be killed?
He must choose a character that can actually be killed. Since Tywin can not be killed, he also can't be chosen to be killed.
Staton said:
He must choose a character that can actually be killed. Since Tywin can not be killed, he also can't be chosen to be killed.
Does this also apply to Deadly or would Tywin be an acceptable choice there?
It applies to all effects that would kill Tywin. Deadly, Die by the Sword, anything that actually kills. Tywin can't be killed by those effects, nor can he be chosen for them.
The word "cannot" is "absolute", according to the F.A.Q. in this game. It cannot be superceded by any means.