In a large bowl, beat together the peanut butter, softened butter, and vanilla extract until smooth and creamy.
Add the powdered sugar and crushed pretzels. Mix until a thick dough forms.
Scoop about 1 tablespoon of the mixture and roll into balls. Repeat with the remaining mixture.
Place the peanut butter balls on a parchment-lined baking sheet and chill for about 30 minutes, or until firm.
In a microwave-safe bowl, melt the chocolate chips and coconut oil in 30-second intervals, stirring between each interval until smooth.
Insert a toothpick into each peanut butter ball and dip into the melted chocolate, leaving a small circle of peanut butter exposed at the top.
Let the excess chocolate drip off, then place the buckeyes back onto the parchment paper.
Sprinkle with flaky sea salt before the chocolate sets, if desired.
Let the buckeyes set at room temperature or refrigerate until firm.
Store in an airtight container in the refrigerator for up to 1 week.