Lay cake on a clean work surface. Mix the whipped topping and vanilla extract together until combined. Spread white frosting over the top of the cake to coat completely. Roll up the cake, jelly-roll style, and then cover the outside of the cake with the frosting. Drag a fork along the length of the cake to form a bark design. Dust with cocoa powder and refrigerate.
For the forest mushrooms, insert 1 toothpick through each marshmallow and then into the flat side of the chocolate kiss to form "mushroom." Group chocolate mushrooms along cake by inserting toothpicks into surface of cake, at intervals to resemble growths of forest mushrooms. Dust chocolate kiss candies with confectioners' sugar. Slice and serve.