Grease the bottom and sides of a 9x13 pan with butter. Melt butter in a large pot over medium heat. Add marshmallows and vanilla extract. Stir in matcha and continue to cook until marshmallows are melted.
Turn heat off and stir in Rice Krispies until thoroughly coated in matcha marshmallow.
Spread evenly on pan using a buttered spatula or lightly greased fingertips to press. Firm at room temperature for 30 minutes.
Melt chocolate chips and coconut oil in a saucepan over medium-low heat, about 5-7 minutes. Stir well.
Slice Rice Krispies treats into squares. Dip the top of each treat in chocolate and place on a wax paper lined cookie sheet. Add remaining chocolate to a sandwich bag and cut off the tip.
Add a dot of chocolate to the back of candy eyes and place on each treat. Design a stitch mouth on each treat. Allow chocolate to firm in the refrigerator for 20 minutes. Store in an airtight container.