Hand of Fate

The Demon Trader will give you unlocks in exchange for some of your blessings. Your first encounter, he will ask for one blessing, II-V will require two blessings, and for VI, he will demand THREE blessings.

You should have one blessing to start with, granted by a trophy from the dealer (the Pentacle, specifically). For the other two, you can either buy them from Call for the Priest if you run across it or from encounters. The ones you should try to include in your deck as they usually grant a blessing:

The Maiden
Wandering Minstrels (ask them to play a song, sometimes gives two blessings)
Desert Cult (offer your blood)
The Altar
Helpful Priest (give him half your food, Huge Success grants two blessings)
Devil's Carnival (requires Huge Success x2)

If you play with the King of Skulls as the boss, you can also come across the Hanged Man encounter, which will give you a blessing as well as a curse. However, this is not recommended as you begin that adventure with the Corrupted Soul curse, which reduces your max health by 10 for each new curse, so it's usually better to avoid the Hanged Man if possible.