This is a puzzle that I use with my Spanish 3 class after we have learned eight tenses (present, preterite, imperfect, future, conditional, progressives, perfects, commands). They must match an edge with a subject and verb to an edge with a conjugation - in any of the eight tenses - in order to form the 4x4 square.
For this activity, I have my students work in pairs, so I print enough puzzles for half of the class. Then, I cut them apart the night before & put them in a baggie or paperclip them in sets. Each pair is given one set of pieces, and they must figure out how to form the 4x4 square. Once they figure it out, they glue it on a piece of construction paper for grading or display. It is great, as the teacher, to hear them discussing what tense they see and whether it is a valid conjugation for the subject/verb combination provided.
Oh, and the "key" is the actual handout, since you must cut the squares apart before giving them to the students. Just print an extra copy for yourself, and you have the key!