Line a 12-cup muffin tin with paper liners and set aside.
In a medium saucepan over medium heat, stir together corn syrup and brown sugar. Bring to a gentle boil, then remove from heat.
Stir in the peanut butter and vanilla until smooth.
Add Cheerios and mix until evenly coated.
Spoon the mixture evenly into the prepared muffin cups and gently press to pack.
Melt chocolate chips and 1/4 cup peanut butter together in the microwave in 20-second intervals, stirring until smooth.
Spoon or drizzle the chocolate mixture over the Cheerios cups.
Chill in the refrigerator for 1 hour or until set.