Sign in Blood
While the one mana instant is certainly very powerful and flexible, especially in the current ETB-heavy metagame, it does nothing on its own
Seedborn Muse and Vedalken Orrery are already annoying to play against because of how powerful they are, and Prophet of Kruphix combines those effects into one card
If a cards health falls below zero it must be discarded, with damage carrying over between rounds
Fallout Dogs: Dogmeat, Ever Loyal and Rex, Cyber-Hound I'm sure I've said it before, but Fallout is my favorite video game franchise, and I would be remiss if I didn't include the two quintessential Fallout dogs in this list
2: Create two 1/1 black Nightmare creature tokens with "At the beginning of combat on your turn, if a card was put into exile this turn, put a +1/+1 counter on this creature." 7: Target player exiles the top X cards of their library, where X is the total mana value of cards you own in exile