Preheat the oven to 350F.

Using a paring knife, cut lengthwise through 1 end of each hot dog, about one-third of the way up.

Rotate hot dogs and cut down perpendicularly to the first cut, to create four "tentacles" (these cut ends will curl up to look like tentacles when the hot dogs cook).

Bring a large pot of water to a boil.

Blanch kale leaves one or two at a time until pliable, 20 to 30 seconds.

Transfer to a paper towel-lined baking sheet to drain well.

Add hot dogs to the pot and simmer until "tentacles" curl and separate, 2 to 3 minutes.

Transfer to the baking sheet with kale.

Cut each kale leaf into two or three long pieces and wrap them around each hot dog, weaving them through the "tentacles"

On a clean surface, spread each piece of crescent roll dough with some of the mustard, top with a hot dog, and roll up snugly.

Arrange on a parchment-paper-lined baking sheet and bake until puffed and golden brown, 16 to 18 minutes. (Bake a day or two in advance and reheat in a 300F oven until hot, if you like.)

Using a paring knife, cut out slits for your sea monsters' eyes and mouths (or make slits and insert small pieces of the kale stems for eyes).

Dot "tentacles" with relish "sea slime" and serve with ketchup for dipping.