Progression & Persistence
What a game remembers about you between deaths and sessions, from three initials in Asteroids to a battle pass that expires on a schedule.
Numeric Score in Pong is the first thing a game ever remembered, and the whole family is downstream of that impulse to keep a number. Space Invaders converts failure into a budget with Lives and Continues; Asteroids writes the number to battery-backed RAM and invents both persistent identity and the leaderboard. Rogue then does two incompatible things in the same year — Experience Points and Levels imports permanent capability from tabletop, and Permadeath Run Structure guarantees you will lose it.
Hardware settles the argument temporarily. Pitfall II's Checkpoint Respawn makes failure a rewind. Metroid encodes state as a password the player carries; The Legend of Zelda's Battery-Backed Save File makes the cartridge remember, which is what makes the modern campaign possible. Diablo's Branching Skill Tree and Colour-Coded Loot Rarity turn progression into a spatial choice with opportunity cost and a one-glance value language, and World of Warcraft compresses that language back into a single ascending number.
Designers argue endlessly about what death should cost. Dark Souls answers with Bonfire Checkpoint & Currency Risk: rest resets the world, death drops your souls where you fell, and you get exactly one attempt to recover them. Rogue Legacy answers with Run-Persistent Meta-Progression, where the run is lost but something survives it — the compromise that made roguelikes mass-market. Call of Duty 4 answers a third way, with Prestige Reset-for-Status, where surrendering everything voluntarily is the reward. All three are grandchildren of the same 1978 decision to charge for another life, and all three are still in active dispute.
The family, in order of arrival
Every mechanic in this family
Inherited from other families
Mechanics outside this family that parent something inside it — where the cross-pollination happens.