Enemies indicate their intentions before acting: a sword symbol means they're going to attack (their exact damage shown by a number), a shield means defend, a purple swirl means they're preparing to hit you with a status effect, etc. After a player finishes their turn, the enemies act, any unused cards in the player's hand are discarded, and a new round begins.

This simple loop becomes increasingly elaborate as additional cards are acquired. After each battle, players have the option to add new cards to their deck. These choices are mainly drawn from a catalog of 75 class-specific cards, but 56 “colorless” cards turn up in events and shops, and 14 “curse” cards can be inflicted on a deck through various means. Of course, as in any tabletop deck-builder, removing cards can be just as important as adding new ones; opportunities to do this are rare, coming erratically through random events or purchased at shops for increasingly steep prices.

MegaCrit co-founder Anthony Giovannetti comes from the Android: Netrunner card game scene. Netrunner's focus on flavorful, asymmetrical factions finds a parallel in Spire's class card sets. Each class starts with a basic deck, comprised mainly of rudimentary attack and defense options, alongside a few more advanced cards that indicate a class's particular specialties and suggest directions in which the deck can be built. These inherent possibilities are further enhanced by relics, which are non-card items acquired through questing that provide passive benefits.

Each class favors certain overarching tactics, implied by its card set and internalized over time through repeated playthroughs; for example, the wizard-like Defect likes to specialize in one of several elemental magics. But the random elements brought about by the roguelite DNA ensure that every deck, even when it adheres to familiar strategies, feels unique.