Actally, based on those criteria we used to determine the worst card over all, the worst card would be Martyr's Tomb.
It can't win the game; it can't even delay losing very well.
And, unlike the other sucky cards you people are mentioning, there is no chance for this card to have hidden potential (except possibly with some creature that gives you exorbitant amounts of life but has low toughness. Nothing in Type II right now is like this - the closest is Gerrard, and 4 toughness is pretty big.).
Duel, I realize that False Dawn is better, mainly because it's a cantrip. However, if I'm correct, this was your reasoning:
1: It's a cantrip.
2: It's good, because it's a cantrip.
3: It's helpful, because it's a cantrip.
4: The rest of the stuff in the spell just might be good too (although of course the drawing a card is better).
That's a little... um... redundant.