Place the eggs in a large pot. Fill the pot with water so that it completely covers the eggs. Heat the pot over high heat and bring the water to a boil. Turn off the heat and cover the pot with a lid. Let the eggs sit in the hot water for 10 minutes.
Strain the eggs from the water and submerge them in a bowl of ice water. Allow the eggs to cool in the water for about 7 minutes then peel the shells off.
Slice the eggs in half, lengthwise. Use a spoon to remove the yolks from the center and reserve them in a bowl. Cut half of the sliced eggs in half.
Use a fork to mash the egg yolks until they become fine crumbles. Add in the avocado and mash until there are not more chunks. Add in the mayonnaise, yellow mustard, and salt to taste. Mix with a rubber spatula until smooth. Transfer the filling to a piping bag fitted with a circle tip.
Slice the celery stalk at an angle so that you form triangular shaped slices. Reserve the celery for later.
Fill the cavities of the 6 egg halves with the filling so that you form a small mound. Place two black peppercorns onto the filling to make the eyes. Then place a celery slice on each side to form the ears. Place one of the quartered eggs on top of the “head” to form a dome. Enjoy!