Heat oven to 350ºF. In a large bowl, cream together sugar and butter until light and fluffy. Add the eggs, one at a time, and mix well after each addition. Add cocoa and food coloring to sugar mixture and mix well.
In a small bow, mix together flour and salt. Add flour mixture to the wet ingredients alternately with buttermilk and mix until combined. Mix in vanilla extract.
In a small bowl, combine baking soda and vinegar and add to the large bowl. Pour batter into greased 9x13-inch pan. Bake for 35 minutes, or until a toothpick inserted into the center comes out clean. Cool completely.
While the cake is cooling, for the frosting, in a large bowl beat together cream cheese and butter together until smooth. Add marshmallows and powdered sugar and beat until smooth. Fold in coconut.
To make truffles, break up cake into a large bowl. Add frosting and mash together until thoroughly combined and smooth. Roll one scant tablespoon of filling into balls and place on baking sheet. Refrigerate while you prepare the chocolate.
Line a baking sheet with parchment. Using one bag at a time, melt bag of chocolate in a medium bowl. Add vegetable oil and stir to combine. Place one ball at a time in chocolate, turning over with two forks, and remove to baking sheet. Immediately decorate with sprinkles or melted chocolate. Let set and repeat with remaining cake truffles.