The Amazon
Spoiler: this page reveals the child’s secret move.
If you are the grown-up in a family, play first — the whole point is that the child shows you. If you came here from a search about the Amazon piece, read on.
Reveal the rule
The Amazon is a chess piece that is not in the standard game. It moves like a queen — any distance along a row, column or diagonal — and it can jump like a knight: two squares one way, one square sideways, over anything in between.
Chess players know it from puzzle variants (it is sometimes called a maharaja or superqueen). Most grown-ups have never seen one. That is exactly why AhaMate gives it to the child.
Dots: queen lines. Yellow rings: the knight jumps.
Why it is the child’s secret
In the first mission the child saves the king by blocking. In the second the child is shown the jump and captures a guard with it. Later the child chooses one of three traps. In the hardest one the grown-up sees a queen-looking piece and tries queen moves — which are all blocked; the only way out is the jump the child has already made. The other two traps can be solved without the jump, and the child’s reveal shows the jump anyway.
One rule, honestly stated
On our 5×5 board the Amazon’s queen lines stop at the first piece in the way, like a real queen. The knight jump ignores pieces in between, like a real knight. That is the whole rule. The game’s chess logic is checked against a separate oracle so what the child is shown is correct chess, not a cartoon of it.