Put boiling water in a heatproof measuring cup. Add green tea and yerba mate and steep for 5 minutes. Remove the tea bags, squeezing the excess liquid into the cup before discarding.
Stir in sweetener and lemon juice. Add 6 ice cubes and stir until they are melted and the drink is cold. If desired, wet the rim of your serving glass and coat with chopped mint. Add more ice to the glass and pour in the energy drink