First, I will post some new art.
And now we go to confusing pre-release information. I will try to make this as simple as possible.
For each Theros set there are 3 "quests". The final is a match against a challenge deck. For each quest you play in you get a different Hero card. The first quest is the pre-release and as far as I know you do normal events and get a Hero card. The next "quest" is during the release weekend. Aside from normal events you get so try to see the "answer" in a poster.
Once you know the answer you get your second Hero card. During the Theros game day you get to fight the Hydra. This Hydra is a special deck constructed to try to beat you. You fight it by using your Standard deck and playing a game. You have to destroy all the Hydra's heads without being defeated. There are 2 special Hydra cards, a head and a sorcery. These cards have special backing.
If you defeat the Hydra, you get the third Hero card. If you get 9 Hero cards (3 for each set), you get a special reward. I hope that all of this made sense to you because it does not to me.