First of all I want to say I think the collector is awesome...but perhaps too awesome.

I just finished Ascension 20 with few decent relics and IMO a very sub-optimal deck.
I am approaching 1000 hours in StS as a whole; I play for fun and I'm not much into min-max theory crafting...with that said below are some of my thoughts:

• You are MINE - Might be a bit too strong, maybe drop the DOOM amount from 12 to 10.
  
• Dark Lord Form - Probably should cost 5 energy and upgrade to 4 energy (ethereal status should stay).
  
• Omen - Really strong card, drop damage from 10 to 8 (maybe even lower).
  
• Whomp - Reduce damage and hp gain 12 to 10 (upgraded from 15 to 13).
  
• Thorn Whip - Essence gain of 9 is quite high 6 might be more balanced.
  
• Dragon's Trove - Probably should be draw 1.
  
• Dark Apotheosis - Probably should cost 2 (1 when upgraded).
  
• Raging Call/Binding Call/Protecting Call - Drop all effects by 1 (ie gain 5 temp HP. Torchhead gains "gain 1 block")
  
• Suckerpunch - I would remove this altogether and replace with a Kindling that causes Weak.
  
• Sombre Shield - drop block gain from 6 to 5.

Collection deck seems pretty balanced, I don't have any notes on those.