Unroll your crescent dough onto a clean, lightly floured surface and press together any perforated seams so you end up with one solid rectangle. Using a sharp knife or pizza cutter, slice the dough lengthwise into thin strips, about eight per hot dog is plenty. Set the strips aside while you prep the hot dogs.
Take one strip of dough and start winding it around a hot dog, stretching it gently as you go so it holds its shape. Crisscross the strips loosely rather than wrapping too tightly, since real mummy wrappings always look a little messy and uneven. Leave a small gap near one end of the hot dog uncovered for the face.
Place your wrapped hot dogs on a parchment-lined baking sheet, spacing them about an inch apart so the dough has room to puff up. If you're using melted butter, brush a little over the top of each one now. Bake at 375°F for 12 to 15 minutes, until the dough turns a light golden brown.
Once your mummy hot dogs have cooled for a few minutes, dip a toothpick into the mustard and dot two small eyes onto the exposed part of each hot dog. This is the step that really brings the mummy look to life, so take your time and have fun with it.
Arrange the finished mummy dogs on a serving platter alongside small bowls of ketchup and extra mustard for dipping. They're best enjoyed warm, right when the dough is still soft and the hot dog is juicy.