Butter a 9x13-inch baking pan. Line a baking sheet with parchment paper.
Melt 1/4 cup butter in a deep saucepan over medium heat, about 3 minutes. Stir. Add marshmallows and stir until melted, about 4 minutes. Add crispy cereal and stir quickly to evenly coat the cereal.
Spread an even layer of marshmallow mixture into the buttered pan. Let crispies sit at room temperature for 30 minutes.
Combine chocolate chips, oil, and salt in a heatproof bowl. Place bowl over a saucepan containing a few inches of water over medium-low heat. Bring water to a simmer. Cook and stir chocolate mixture until melted, about 3 minutes. Add matcha powder, stirring until evenly mixed. Remove from heat.
Cut crispies into 24 equal pieces using a sharp knife. Dip 1 end of each bar into the chocolate-matcha coating; place on the parchment-lined baking sheet. Refrigerate for exactly 10 minutes, or bars will lose their crispiness.
