Cream the butter and brown sugar together in a stand mixer with the paddle attachment, or use a hand mixer, until the mixture is light and fluffy, then beat in the egg and vanilla until smooth.
Add the pudding mix, baking soda, and salt, and blend until just combined, then mix in the flour until a soft dough forms.
Stir in the sprinkles and chocolate candies with a spatula until they’re evenly distributed, then scoop the dough into 2 tablespoon-sized balls and place them close together on a baking sheet lined with parchment paper.
Cover the tray and chill the dough balls in the refrigerator for at least 30 minutes so the cookies don’t spread too much while baking.
Preheat the oven to 350°F (175°C), then arrange the chilled cookie dough balls 2 inches apart on prepared baking sheets and bake for 9 to 11 minutes until the edges just start to turn golden.
If you’d like, press 1 or 2 candy eyes and a few extra chocolate candies into the tops of the warm cookies right after they come out of the oven, then let them cool for 5 minutes on the sheet before transferring to a rack to cool completely.
Store the cooled cookies in an airtight container at room temperature for up to 4 days or freeze them for up to 1 month.