Sliding Puzzle

Sliding puzzles are a type of spatial puzzle in which a set of pieces are set into a space where they can be slid around along one or two axes, but with limited space to move them. The goal of such a puzzle is often to recreate an image or arrangement of the pieces, but can also be to allow a particular piece to exit the space from a specific point.

Background
Sliding puzzles are a common puzzle type found in video games, with the genre being found in many different variations across the puzzle game series Professor Layton.

Puzzle Application
Most traditional sliding puzzles take place in a square space, with equal-sized tiles filling all but one section of the available space. These tiles can have several different things printed on them to help indicate what the correct solution is: numbers, letters, parts of a picture, or just different colors. The tile design tends to be chosen to best fit what the goal of the puzzle is, both as a solution and as a setpiece within the puzzle. Artwork, numbers, and letters can all play the same role by indicating an order for the tiles to take (1-?, A-?, or just forming the picture). Letters can also be used to form words within the grid, allowing for interplay with other word puzzle genres or alternative final formations.

Some sliding puzzles, rather than just having a final layout signifying that the puzzle has been completed, revolve around trying to move particular 'special' pieces to certain spots (regardless of the non-special pieces' positions) or free a particular piece and move it out a predetermined hole.

Sliding puzzles are common as physical objects, but can easily be recreated digitally or provided in a static form thanks to the ease of creating an informal version out of pieces of paper.

Strategy
With square, two-dimensional sliding puzzles, one strategy for completing entire rows at once is to attempt to get the row's pieces in order, but adjacent in any direction. By doing this, the sequence can be snaked along one space at a time and travel through the entire row until it has been placed correctly. This strategy works best when performed using the top row or first column.

Examples

 * - A very traditional slide puzzle, albeit in unmovable form. Rather than giving teams an actual slide puzzle to work with, this puzzle just tells them the original arrangement of tiles and the desired final state. Solver have to simulate it on their own, and keep track of the moves they make to extract their final answer.
 * - A more modern version of a slide puzzle, taking place entirely digitally. However, this also allows for it to be a bit tricky, with each piece scrolling to show bits of six different pieces over time. This makes it very difficult to figure out what goes where, let alone get them to the right spots.