Yes, you can use a 9x13 pan for this reindeer recipe, but the treats will be flatter than the round pan. Simply slice long ways down the center of the Rice Krispies, then slice 7 triangles in the halved Rice Krispies. If you use the 9x13 pan, you will need 28 chocolate-covered pretzels, 14 M&M’s, 28 eyes, and sprinkles. I find that using a 10-inch springform pan to make a round version is larger and easier to extract.