Enemy Troops! Throw your best ideas at me!

[-Perception-]

We already have such enemies, Spawn of Loki, they are most vulnerable at their feet. (Still tough though..)
Apart from that, your idea summarized/generalized:
  A bot with awesome armor and a two-handed sword.
  (The part with "vulnerable only by.." is quite queasy, puts many classes at disadvantage.)

I am sure you think of something better.  (Or design the Fafnir armor..)