The first time you try to play this Tetris-like game, you will probably lose fairly quickly. When you do so, a "high scores" list will pop up showing Mr. E. Hunt with a score of 89999. Your goal, then, is to score 90000 points.
A little experimentation will reveal that you score points as a result of forming lines, and the more simultaneous lines formed, the bigger the score bonus; you get 1 point for forming a single line, 10 points for forming two lines simultaneously, 100 points for three lines, 1000 points for four lines, and finally 10000 points for forming five lines at once, by dropping in a piece which is a column five squares tall.
It turns out that the game gives you a fixed sequence of 90 pieces, and every tenth piece (and no others) are five-square-tall columns. So, the only way to score 90000 points is to assemble each of the nine sets of ten pieces into the bottom five rows of the Pentris well, with the tenth, vertical piece clearing all five rows. There is a unique way to do this with each set of ten pieces.
Some of the pieces are marked with one of three symbols. The image to the right of the applet can be overlaid exactly on the applet frame, with the grid of letters lying over the Pentris well. When the pieces of each subpuzzle are assembled correctly, the marked squares on the pieces correspond to letters in the grid which, when read in order of the subpuzzles (multiple marked squares in a single subpuzzle being read in the order that the types of marks first appear in the puzzle), spell out the answer, ATLANTICSALMON.
The solutions to the individual subpuzzles are below.
2006 MIT Mystery Hunt