Any card that potentially demands multiple cards to deal with is a huge winner in my book
Was it a dead card in my hand for the entire game up to the point where the stars aligned
#6 Sheltered by Ghosts Set: Duskmourn: House of Horror Market Price: $4.09 Sheltered by Ghosts gives players access to the same effect as cards like Banishing Light for a one-mana discount
With that in mind, the same as "Player Characters" and their Backgrounds, Doctors and their (other) Companions, and the more limited Friends Forever and Partner With mechanics, we're going to count Companion as yet another "Partner" mechanic
Cards like Marlboro inflict your opponent with a bunch of effects which make the card so flavorful
Spell Pierce is cheap enough to be viable, but if youre playing enough interaction that you need to get to Spell Pierce, theres a good chance youre making the game go long enough that it wont always work