by Matt Gruskin, Dan Katz, Matto Mildenberger, Stephen Peters, Rebecca Vessenes, and Justin Werfel
Problem:

This looks like a normal version of the memory-matching game Concentration, but it quickly becomes clear that there is a twist: after the solver tries to match a pair of cards, the cards move. After much clicking around, solvers should recognize that the cards always travel along a simple path throughout the 10×10 grid.

When the cards are matched, they disappear, revealing either a letter or a number from negative 9 to positive 9. (If the solver clears the entire board, they will be greeted with the message, “Congratulations! Take a victory lap.” Clearing the board is not, however, necessary to solve the puzzle.)

The letters initially spell out the hopefully helpful instruction to IGNORE FLOWERS. If solvers instead follow the path that the cards use to move, starting at the uppermost R (the first letter along the loop if you begin at the upper left corner), and adjusting the letters by adding or subtracting based on the numbers in the path, the result spells out the answer, EIDETIC MEMORY.

Start Letter Changes End Letter
R -5, -7, +4, +3, -6, +1, -3 E
N +2, -7, +3, -8, +4, +1 I
I -1, +3, -6, +4, -5 D
G +2, +7, -4, +3, -6, -4 E
O +4, +3, -7, +5, -4, +5, -1 T
L -2, +9, +5, -7, -6, +4, -3, -3 I
E -3, +6, +2, +4, -7, +3, -9, +2 C
E +1, +8, -2, +6, -3, -4, +2 M
S -9, -6, +4, -1, +6, -8 E
R +3, -5, -9, +4, +2 M
W -7, -4, +6, -5, -3, +5 O
F +1, -3, +2, +9, +8, -4, -1 R
O -8, +1, +5, +7, -9, +6, -3, +5, +6 Y

This is the initial layout of the cards, before the first guess is made:

This is the content revealed after the cards are removed, with the path of the cards highlighted: