It plays like Binding of Isaac mixed with Hearthstone: You are playing a challenging action game through quick arenas and before each of them you get a card phase where you can use your deck to upgrade your stats and abilities - e.g. letting your whirlwind attack start shooting fireballs in all directions while spinning or giving your ranged strike infinite range, along with another upgrade to make it branch in multiple directions and a third to make its victims explode for area damage.
A battle consists of 8 card phases and arenas, leading up to a tough boss battle. You can combine cards in thousands of ways but you have to balance that with the ability to survive against swarms of enemies and challenging bosses.
The game is fast-paced with battles playing out in 5-10 min. For one of the 3 programs (campaigns), you are playing your way through chambers of 3 battles each to reach the program’s endboss. The battles are randomized each time, although they all have special rules (e.g. “Meteors flying through the arena” or “+1 mana each card phase, but unused mana deals damage”) and you can try to pick those you think you can handle best.
One death and your run is over - although you may have completed some quests and earned gold for new cards that can help you do better next time or give you new fun builds to play with.
Along with the programs, there is ranked play, where several new challenges are generated every day and players compete for rankings in a seasonal leaderboard.
The game has 4 champions, 3 different companions and 3 programs of increasing difficulty and variation. From the second program onwards, the bosses also begin playing cards against you to spice things up.