The Gauntlet of the Gods is a challenge in Ranked mode that rewards successful games with Flux: the crafting ingredient used to increase the quality of your cards.
Winning your first game will reward you with a base level of Flux (amounts indicated here) and begin your gauntlet run.
Each win will earn you a greater sum of Flux, to a total of three wins with each god. But adapting to different playstyles takes practice, so don’t fret if you aren’t yet able to win with different gods. The Gauntlet of the Gods resets on a regular basis, so you can easily begin anew!