"For instance I have a lot of cards that I didn't play that came back and did great once something changed in the new cards. I will use "Nightmare" as an example. He got to be a really good and usable card in certain rulesets once Byz Kitty showed up. There are many other examples of cards that "come back" based on certain new abilities, mana additions, and rulesets added to the game."

Nightmare is no bad card but what use you have f.e. for the Rusty Android ? When you used him last time ?