The Wagner is second by a mile, as the toughest card in the T206 set, but it is the symbol of the the hobby, and the one that I need.
Chances are that it might not come to be in my case, but life is full of surprises.
The Unbelievable we can do ...
the Impossible ... will take a little longer. 
If you're looking for an immortal challenge ... try the
T209 type II set.