Double-cat strategy guide (2★)

Two cats per row, two per column, two per color — still never touching. That is Duckdoku’s double duck mode, and it is exactly the classic 2★ Star Battle ruleset. The board looks the same; the game is not.

Why it needs its own guide

Double-cat is not “the same puzzle, twice.” The single most important deduction of the one-cat game — a placed cat kills its whole row, column, and color — is simply false here. Each line owes two cats, so one cat leaves everything half-alive, and a solver running on one-cat reflexes will scatter wrong crosses across the board. Meanwhile the strongest double-cat techniques are counting arguments that have no one-cat equivalent at all.

If you are coming from Meowdoku, Queens, or 1★ boards, start with the single-cat guide — the golden rule and half the ladder carry over. This page is about the other half.

The double-cat ladder

1. Smaller shadows — a cat now blocks only its eight neighbors; the row dies when the second cat lands. Unlearn this first. (Reflex level)
2. The pair squeeze — anything that still needs two cats can’t clump them: a square that touches all the others has no room for its partner. (Beginner — and the workhorse)
3. The stretch squeeze — a stretch of L squares holds at most ⌈L/2⌉ cats. Count the stretches and lines start forcing cats on their own. (Intermediate)
4. Band counting — colors trapped inside a band of rows account for all of that band’s cats, and everyone else’s squares there die. (Advanced)

What carries over from one-cat play

• Forced moves — the count just doubles: a color with exactly two squares left for its two cats places both at once.
• The row & column squeeze — still valid as written: a square touching every survivor of a cat-less line dies, because at least one of that line’s cats will land next to it.
• The color squeeze — same idea, harsher arithmetic: a cat is impossible if it would leave some color too few usable squares for its remaining cats.
• What-if chains — the last resort is the last resort in every ruleset.

The golden rule, unchanged

Never guess. Every cross should come with a one-sentence justification — and in double-cat the sentence usually contains a number: “this stretch fits one, that stretch fits two, the row needs two.” If your sentence has no number in it, double-check that you aren’t running a one-cat reflex.

Stuck on a real board? Import a screenshot — double-cat boards are detected automatically (two ducks sharing a row or column is all the proof the importer needs), and every hint names the rung of this ladder it came from.