Preheat oven to 350°F/175°C. Line a cookie sheet with parchment paper.
In a mixing bowl, beat vegan butter on medium speed until light and fluffy, about 2 minutes. Add the sugars and beat for another minute.
Beat in the vanilla and the flax egg. Set aside.
In a separate bowl, combine the flour, cocoa, baking soda, baking powder, and salt. Whisk to combine. Pour the flour mixture into the butter mixture. Stir to combine. If the dough seems too crumbly at this point, add 1 tablespoon at a time (up to 4) of plant-based milk and stir to combine.
Add most of the chocolate chips, reserving ¼ cup for the final step.
Drop cookie dough balls by rounded tablespoonful (using a cookie dough dispenser helps make the cookies evenly sized) onto a prepared baking sheet, leaving about 2 inches between each. Press the dough balls gently to flatten.
Bake for 8 to 10 minutes. Remove the cookies from the oven and place and transfer to a wire rack to cool completely.
Once the cookies have cooled completely, melt the reserved ¼ cup of chocolate chips in the microwave (for about 11 seconds, then stir), and using a butter knife or other utensil, place a dollop of melted chocolate on the cookie, followed by a Skittle. Do 3 to 4 per cookie, with different colors. Use the same process to add two googly eyes to each cookie.