Eternal Decks · Board game rules
In eternal decks, can a rare card placed be multiple things for multiple requirements, for instance in Stage C - a line of blue cards, then the next stage it can be a purple?
Quick answer
Yes — a Rare Card isn't locked to one color/number once played, so it can satisfy a blue-line requirement for one puzzle and later be counted as purple (or any other color) for a different puzzle requirement.
Details
Rare Cards are inherently flexible: after being played, a Rare Card "can be considered to be any of the five colors or nine numbers (1-9)" [p.10 — Taking A Turn]. This general flexibility carries over into Stage C's puzzle-solving: "Rare Cards, the Minotaur Ability Card, and the CAMP 4th Lap Bonus Card can be used as any color in a puzzle" [p.33 — STAGE C]. Since the puzzle rules don't say the color is "locked in" the moment it's first used, the same Rare Card sitting in the Field can be re-interpreted as whatever color is needed at the exact moment a later puzzle is completed.
This is supported by the Minotaur example, where a player declares the Ability Card's color ("red") only at the moment of puzzle completion — the color designation is decided on the spot, not fixed permanently [p.33 — STAGE C]. So as long as the card remains in the Field (it isn't cleared until the row itself is cleared), its color/number identity can shift to match whatever puzzle requirement is currently being checked.
Watch out: This flexibility only applies in normal Stage C rules. In Stage C+ (Advanced/Combination mode), Rare Cards, the Minotaur Ability Card, and the CAMP 4th Lap Bonus Card cannot be used to complete any puzzle at all [p.50 — STAGE C+]. Also, once a row is cleared (an Eternal is Revived in that row), all cards — including Rares — move to the Discard Area, so their "flexible identity" only persists while they remain on the Field.