Deck-builder
A deck-builder is a game where every player starts with a small identical deck and acquires new cards during play to build a stronger, personalized deck over the course of the match. Dominion popularized the genre; the cards you buy go into your discard pile, shuffle back, and shape your future hands.
Why it matters
Deck-builders need a market of buyable cards plus a starting deck (usually a mix of weak currency and weak attack cards). Designing one means balancing many cards against each other, not just one fixed set.
Example
A deck-builder might give every player a starting deck of 7 coppers and 3 estates, plus a shared market of 10 unique card piles. Each turn a player draws 5 cards, plays them, buys new ones, and discards everything.