Unique or Legendary prophecy
Sacrifice a hand to chain the wolf.
You will face a challenge with Fenrir's blessing. Defeating this challenge will slow all future challenge creeps by 30%. Fenrir will bite the hand off the tower deals the most damage to the challenge.
Lost hand effect: (hopefully implemented as an effect symbol on the card)
1/2 targets (holgar would only get one ax)
2/3 base damage
Edit: revise to match Andy's prophecy wording.
Tweaked a few parameters for balance:
50% slow = 2x time to walk. Revised to 30% slow, which is ~1.5x travel time.
1/2 base damage is a brutal penalty. 2/3 is more reasonable.
Depending on how useful the effect is and how crippling the penalty is, maybe the slow (or half of it) could also apply to Vir.
The idea is to try to not have your carry lose the hand, but killing a prophecy without much help from your carry is hard.
Since unicorn is a huge damage dealer to challenges, maybe Fenrir would eat the unicorn whole before it could cry. The unicorn usually dies anyway and the lost hand penalty is not a concern.