Slice open each Medjool date lengthwise to carefully remove and discard the pit. Line a small cutting board or tray with parchment paper and arrange the pitted dates on top. Place a second sheet of parchment paper over the dates, then use the flat bottom of a sturdy glass to press down firmly until each date is flattened into a round disc. Remove the top sheet of parchment paper.
Dab one teaspoon of marshmallow fluff onto the center of each smashed date. Gently press two mini salted pretzels into the marshmallow fluff on each date to help them adhere.
Add the chocolate chips and coconut oil to a small microwave-safe bowl. Heat in the microwave in 30-second intervals, stirring thoroughly between rounds, for about 1 minute total until the chocolate is completely melted, smooth, and glossy. Spoon the melted chocolate over the pretzels and marshmallow layer on each date to cover them.
Finish each smashed date with a light sprinkle of flaky sea salt over the wet chocolate. Transfer the tray into the refrigerator for 30 minutes, or into the freezer for 10 minutes, until the chocolate shell sets completely firm before serving.