For the Banana Popsicle Ghosts: Line a large baking sheet with parchment paper or a silpat mat. Peel 2 bananas and slice each in half, cross-wise. Slice each half in half again the "long" way, so that you have 4 long, narrow pieces total. Carefully insert a popsicle stick into the bottom of each, then place on the baking sheet.
For the Banana Popsicle Mummies: Cut the pointy tips off of the 2 remaining bananas, then slice the bananas crosswise into 3 equal round "logs." Insert a popsicle stick into one end of each, then place on the baking sheet. Freeze all banana pops for at least 30 minutes or overnight.
In a small bowl, mix together the yogurt and powdered sugar. Once the bananas are frozen, dip them into the yogurt mixture, then return them to the lined baking sheet. Place 2 mini chocolate chips on each of the ghosts for eyes. Do not place the eyes on the mummies yet. Return to the freezer for at least 1 hour to allow the yogurt to set.
For the mummies, place the peanut butter in a small, microwave-safe bowl, then heat until smooth and creamy, about 30-45 seconds, stirring as needed. With a small spoon, drizzle on top of the banana mummies to make "bandages." Place mini chocolate chips for eyes. Return to the freezer until the peanut butter is firm, about 30 additional minutes. When ready to serve, let the banana popsicles soften at room temperature for a few minutes. Enjoy immediately, or place in a ziptop bag and freeze for up to 2 months.
Freeze leftover banana popsicles in a ziptop bag for up to 2 months.