Put the cereal in a large bowl. Combine the sugar and cocoa powder in a large resealable plastic bag.
Combine the chocolate and butter in a small bowl set over a pot of simmering water. Heat, stirring occasionally, until melted.
Pour the chocolate mixture over the cereal and toss to coat thoroughly. Transfer the cereal to the plastic bag and shake well to coat in the sugar-cocoa mixture. Pour the cereal into a clean bowl and stir in the cherries and pistachios.