01 - Whisk together milk, cream, sugar, cocoa powder, and salt in a medium saucepan. Heat over medium heat, stirring frequently, until hot and sugar dissolves completely. Do not boil.
02 - Remove from heat and stir in vanilla extract until fully incorporated.
03 - Pour mixture into Ninja Creami pint container. Cool to room temperature, cover, and freeze for at least 8 hours or overnight until solid.
04 - Process frozen base in Ninja Creami using the Ice Cream setting.
05 - Create a well in center of ice cream. Add marshmallow fluff, caramel sauce, and chocolate fish or pieces.
06 - Reinsert pint and run Mix-In setting to swirl toppings. Serve immediately for soft-serve texture or freeze 1-2 hours for firmer consistency.