Line a 9×9 inch pan with aluminum foil or parchment paper and spray with nonstick spray.
In a medium-large pot, melt butter over medium-low heat.
When the butter is melted, reduce the heat to low and add 5 cups of the mini marshmallows. Stir frequently until the marshmallows are melted.
Remove from the heat and stir in the vanilla extract and the remaining 1 cup of marshmallows. Stir to melt the marshmallows a bit (chunks of marshmallows are ok) then stir in the gluten free crispy rice cereal.
Once all the cereal is coated with the marshmallow, transfer the mixture to the prepared pan.
Let it sit in the pan to cool for a minute or two then use a spatula or your hands (sprayed with nonstick spray) to press into the pan.
Cool completely then cut into 15-20 squares.
Melt the candy melts in a microwave-safe bowl in 15-second increments, stirring between each heating.
Dip the treats into the melted chocolate or spoon the candy melts over the Rice Krispy Treats. Stick the eyeball candies on top and allow to set and harden on wax paper or parchment paper before serving.
