In a large bowl, combine the green jello mix and 1 cup of boiling water. Whisk until the Jello is fully dissolved, about 2 minutes.
Add ½ cup of cold water and ½ cup of vodka; whisk to combine.
Carefully pour into shot cups, filling them about ⅓ of the way. Chill in the refrigerator until the layer has set, about 45 minutes
In a second bowl, combine the pink jello mix with 1 cup of boiling water and whisk until dissolved. Add ½ cup of cold water and ½ cup of vodka; whisk to combine. Set aside to cool for 15 minutes at room temperature.
Once the green layer has set carefully pour the pink jello mixture on top. Leave some room at the top for the gummy.
Chill in the refrigerator for 2 hours, or until fully set (overnight works too).
Before serving, top with a watermelon gummy.
Notes
Store in the refrigerator for up to 3 days. Make them kid-friendly by replacing the vodka with cold water.