Line an 8 inch square pan with parchment paper and set aside.
In a large pot, heat the butter on medium heat. Once the butter melts, add the marshmallows and stir. As it starts to melt, add salt and matcha and stir.
Turn the heat off and add the puffed rice. Stir until all the puffed rice is coated in the matcha mixture. Pour it into the prepared pan and press it into the pan.
Once it cools down to room temperature, chill it in the fridge for at least 2 hours.
Cut the matcha rice crispy treats into 12 pieces. Dip the tops of each piece in melted chocolate, and set it on parchment paper to let it set. Use a little melted chocolate to glue on the candy eyes. Pour the leftover chocolate into a resealable bag and snip a little bit off the corner and pipe on some mouths and eyebrows.