Every hard shelf now hands you a hint of its own. The first hint on a hard shelf is free, and you get it back when you start over or move on to the next shelf. It no longer comes out of the hints you have saved, which stay for the normal levels and the daily. When you are out of hints, the button now says AD rather than 0, and a hint you watch a video for appears straight away instead of waiting for a second tap. Nothing else changed in this one.

Three free undos on every hard shelf, not one. One undo bought you a single experiment and then started charging. Three is enough to actually work through a bad read of a settling board — take a move back, try the other branch, and take that one back too. The button counts them down, and a fresh shelf or a Start over hands all three back. After that an undo still costs a video, the same as before. Also in this one: taking a move back no longer sends the shelf to the top. The late hard shelves are eleven rows and taller than the screen, so you read them by scrolling, and every undo threw the board back to the first row. The shelf now stays where you were reading it.

Hard mode is harder, from the fourth shelf on. The boards are bigger, they reach full height much sooner, and far more of the moves open to you at the start will lose the shelf - on the old ladder you could often begin by tapping at random and get away with it. The first three hard shelves are unchanged. They are still where you learn that things fall. Also fixed: finishing a shelf could offer you a material you had not actually unlocked, which then refused to be worn.

Hard shelves now use the full width of the screen. They were being sized to fit their height, which left them narrower than every other shelf in the game, sitting inset with a gap down each side. Ask for a hint or an undo when there is no advert to show and you now get it anyway. An empty advert slot is our side failing, not yours. And the undo count on a hard shelf now means what it says. Every shelf gives you one undo free, and after that one costs a video - which is what the button has been showing all along. It was never charging.

Hard mode. It opens after five levels, and on a hard shelf things fall: take a box out and whatever rested on it drops into the gap. An order there can be wrong, not just slow. Every shelf can still be cleared; being stranded costs no life. 120 hard shelves and then it keeps going, twenty more materials to earn on them, thirty more trophies, and two more awkward boxes. Also: long shelves open faster, and a hint now rocks the box it means instead of a quiet ring.