Episode 30 of The Witness keeps working with the three-pointed negation mark. Basket clears a big gray grid with several rules on it at once, then pokes at a machine that throws out a cloud of green sparkles, the fairy dust of the title. Then come an elevator, a laser, and a basement under a windmill. The video ends with one of two doors there left alone.
Everything at once
The video opens at a panel with green and red squares, a start in the middle and a negation mark. The first line is "not really a solution," but a second one lights the cable. The next panel is a gray grid with "a bunch of starting spots, things we had to cover, one negation object, and a bunch of colors we needed to keep not mixed." The trouble is choosing what the mark gets spent on. "I think this one will have to be spent on that." Several long routes fall apart near the top before a new one works. "Aha! We can do this. I think it solves it."
Fairy dust
The cable leads to two small screens that "control these different things from inside of here," and "you only have one or the other." A solve sets off green sparkles over a long table. "What does that do? Wow! That's trippy." The commentary calls it "magical dust... fairy dust." Later Basket sends the dust the other way. "It's all fairy dust in that direction. Not sure what that does, but it's fine."
The laser box
Another cable runs to an elevator, and a green panel on it takes Basket down. Along the rails is what the commentary calls "the laser box," an orange panel between two gray doors. Several lines leave the mark with nothing to cancel until "Oh wait, aha! We can negate that." The line goes yellow, and a laser rises out of a yellow box and fires.
Two panels on an orange wall
Down the path, a blue panel and then a yellow one with L shapes guard a pair of doors. "We need to enclose these shapes." Both go through. "So now we unlock those doors."
Under the windmill
The commentary heads for the windmill, "one of the first puzzles that I said I don't understand." A hexagon panel in the basement is left for later. A green door panel there holds white squares and two negation marks, and it is solved quickly: "I think it's good. Yes. Good."
Where it ends
"Because I'm a completionist," Basket tries the door on the other side too, a panel with yellow shapes and black squares. It does not come together. "We have a choice of two doors, and I don't know if it's important to do both. So I'll leave it the way it is." Basket walks out up a dark passage toward the light, and the video cuts to the end card.