A four-in-a-row line-drop game with the rules turned inside out, three in a row disappears, so the only way to win is a four nobody saw coming.
Take turns dropping discs into columns. A connected line of four still wins, but a line of exactly three instantly deletes those discs and the stack above them collapses to fill the gap. That means you can't just stack three and extend it; you have to engineer a single drop that bridges two separated pairs into a four.
The column drop is Connect Four's, from 1974.
The original rule is destructive: exactly three in a line deletes those discs and collapses the stack above them, so you cannot build a three and extend it.
That closes off the parent game's main technique. Connect Four is won by growing threats until two of them cannot both be answered; here growth is punished, so a four must arrive whole — engineered as a single drop that bridges two separated pairs.
Linkfall is an original free browser game that inverts the classic four-in-a-row line-drop genre, using a collapsing three-in-a-row rule to demand setups instead of straightforward stacking.