The challenge in question is this one, which is solving a couple 4x4 sliding puzzles (also known as 15 puzzle) with the least amount of moves in a certain time limit.
I posted an answer that computes optimal answers within the time limit, essentially ending the challenge. Such an answer is not possible in 5x5 puzzles and higher. And especially in large puzzles, e.g. 8x8 or 10x10 you need techniques that are approximations.
Since the challenge is 5+ years old, is essentially closed, and has an interesting extension into bigger sizes, would it be allowed to repost the challenge for those bigger sizes?