Chill 4 martini glasses. Rim each with a lemon half and then dip in sugar. Squeeze into a shaker the lemon juice from the halves you used to rim the glasses. Place the peppers in the shaker and muddle. Add to the shaker: mandarin vodka, orange juice, cranberry juice and simple syrup. Top with some ice, shake and strain into the glasses. Garnish each with a couple of small slices of serrano pepper.
Combine the sugar and 1 cup water in a small saucepan and bring to a boil. Stir until the sugar dissolves. Remove from the heat and cool. Add to drinks or desserts.