Echoform

Duplicates target plot and all its stats to one empty adjacent plot.

How players use it

Camp Migration, Echoform and Slime count as placing a card on an empty plot (Patch #13), so moving a plot next to a Camp fires it. Since Patch #24 a Camp also triggers when it is placed.
Rainbow cards by job Copies and merges: Echoform duplicates a plot with all its stats onto an adjacent empty plot; Extraction destroys a plot for 5 copies of its card; Codex returns copies of a tome used on it; Singularity (1.0) merges every identical card into one, summing stats beyond any cap; Unify merges the adjacent troops’ units into the target.
Needing many copies of one card You only hold a card’s copies that you were dealt, so these need a way to multiply them. The usual tools are Clone (King of Nature), Echoform and Extraction (Rainbow), and fighting the king who owns the card so it appears as loot. Low difficulty gives you more years to collect.

Loot after beating the Jack of Rainbows (twice per run).
Merchants have a chance to stock one; the Lucky perk and Rare Goods decree raise it.
Gacha at max level, Diffract and the Refraction decree give random Rainbow cards.