Evil Sudoku

Evil is the hardest tier: the fewest givens and an arrangement that defeats every simple move, so you must chain advanced techniques to make progress. Nothing about the rules changes — there is no maths and still exactly one solution — but an evil board can demand fish patterns and colouring where expert needed only pairs and wings.

Evil grids call on the whole toolkit: the X-Wing, Swordfish and Y-Wing, plus simple colouring and the unique rectangle. You rarely need all of them on one board, but a stuck evil grid is always waiting for one specific pattern. Build them up on hard and expert first, then come back. Full toolkit: tips & strategy.

The tiers are a ladder of fewer givens and deeper chains: hard needs the odd advanced move, expert needs them regularly, and evil may require fish and colouring to finish. If evil is a grind, it is not a wall — drop a level, drill the techniques, and climb back up.

The two technique families that separate evil from expert sound exotic and are not. A swordfish is just an X-Wing grown one size: a digit confined to at most three cells in each of three rows, all falling in the same three columns — the digit is then locked to those columns, and every other candidate for it in them dies. If you can scan for X-Wings, you can scan for swordfish; there is simply more board to hold in view.

Simple colouring works on one digit at a time. Wherever that digit has exactly two candidate cells in a unit, the two are linked — one true, one false. Chain those links across the board, marking cells in two alternating colours, and contradictions surface: two same-coloured cells in one unit prove that whole colour false everywhere. Any cell that sees both colours also loses the digit. Colouring is the closest thing evil has to a master key, and it turns boards that look like guesswork back into deduction.

Evil boards open slowly by design — a strong start is often just two or three placements, and knowing that keeps you from doubting the board. Take full candidate notes immediately; there is no scanning phase worth speaking of. Then work the elimination ladder from cheap to dear, and each time a technique fires, drop all the way back down to singles before climbing again — the cascade after a swordfish is where the real progress happens.

Two habits matter more here than anywhere: never guess, because a wrong guess on a board this sparse can survive twenty moves before it surfaces, by which point the game is unrecoverable; and take the uniqueness guarantee seriously — every board here has exactly one solution, so a stall is always a missed elimination, never a broken puzzle. When truly stuck, the step-by-step solver will name the exact technique you overlooked, which is the fastest way to add it to your repertoire.