Add all the old-fashioned rolled oats, creamy peanut butter, ¼ cup raisins, chopped nuts or seeds, and coconut shreds (if using) to a large bowl. Using your hands, mix together thoroughly.
Roll the mixture into small balls with your hands, making each about the size of a tablespoon. Place the balls on a baking sheet with a silicone mat or parchment paper.
Put the baking sheet into the freezer for 30 minutes.
After the trail mix balls are removed from the freezer, melt the chocolate in the microwave or double boiler and stir until smooth. Dip each ball into the melted chocolate until completely covered, and place them back on the baking sheet. If using, add sprinkles or finely chopped nuts on top of the melted chocolate.
Eat immediately, and store any remaining Trail Mix Peanut Butter Balls in an airtight storage container in the refrigerator for up to 5 days.