Bad cards (IMO) that haven't been mentioned:
Hint of Insanity
Tombfire
Mudhole
I should explain my criteria for worst card. The worst card:
1. Can't deal damage. This leaves creatures out of the mix.
2. Can't let anyone draw cards or attack the library.
3. Can't help win the game.
Only a few cards from each set meet these, so in general I try to look for the cards whose effects are least likely to achieve anything.
That's why I included Tombfire and Mudhole. Basically all they do is decrease the chance of threshold, and in my opinion it's not usually a good idea to rely on threshold anyway.
I included Hint of Insanity because it is so situational.
I don't know the statistics, but let's say that on average, only half the time does it make a player discard at all, and usually it's two cards.
So when rounded it makes someone discard an average of 1 card.
This is not worth 2B.
There are other less tangible benefits, like the fact that you get to look at their hand, and the fact that if they had multiple copies of a card, they might really want it, but in general it's pretty bad.
Obviously this could be argued; Odyssey is not a set with lots of cards that rank in the lowest section: Benign (not in my opinion, anwyay).
What do you people think is the worst card in Odyssey?
Also, don't rule out Deserted Temple just yet. Yes, it sucks right now, but a Voltaic Key equivalent for lands might have uses later, and if we don't remember this, we won't be able to make the connection.