Place drink mix in large bowl. Add hot water. Stir until drink mix is dissolved. Add cream cheese. Beat with electric mixer on medium speed until blended.
Gently stir in whipped topping with wire whisk. Reserve 1/2 teaspoon of the cream cheese mixture; set remaining mixture aside.
Crush 3 cookies; place crumbs in shallow dish. Cut cake lengthwise in half. Frost cake top with some of the remaining cream cheese mixture. Place cake top next to cake bottom to resemble a coffin lid. Frost sides and the cut side of the cake top with remaining cream cheese mixture.
Dip marshmallows in water; shake gently to remove excess water. Roll in colored sugar until evenly coated.
Place remaining cookie in center of cake bottom to resemble a body. Line up two rows of 3 miniature marshmallows at bottom of body for legs. Place 2 miniature on side of body for arms. Place large marshmallows at top of body for the head. Using reserved cream cheese mixture, attach 2 miniature marshmallows to sides of head for ears. Use decoration gel to draw a mouth and eyes. Decorate with worm-shaped fruit snacks. Makes 1 coffin cake.