The main body of the Slice Trail Effect.

PositionWidth

private class PositionWidth
{
    public const int timeToDisappear = 3000;
    public Vector2 position { get; private set; }
    public float width { get; private set; }

    private float elapsedTime;

    public PositionWidth(Vector2 position, float width)
    {
        this.position = position;
        this.width = width;
        elapsedTime = 0f;
    }

    public void update(GameTime gameTime)
    {
        elapsedTime += gameTime.ElapsedGameTime.Milliseconds;
        width = MathHelper.Lerp(width, 0, MathHelper.Clamp(elapsedTime / timeToDisappear, 0, 1));
    }
}

SlicerDeluxe

public void update(GameTime gameTime)
{
    //Detect if we have released but not yet begun swiping again
    if (Flame.inputManager.released)
    {
        released = true;
    }
    //get the current input
    if (Flame.inputManager.DRAG)
    {
        SetVerticeColor();
        if (released)
        {
            released = false;
            resetSlicerDeluxue();
        }
        EnqueInput();
    }

    if (positions.Count != 0)
    {
        vertices[0].Position.X = positions.Peek().position.X;
        vertices[0].Position.Y = positions.Peek().position.Y;
        prevPos = positions.Peek().position;
    }
    int i = 0;
    //already set vertice 0 so start at 1
    int currentV = 1;
    //the first positionwidth is the least recent position
    foreach (PositionWidth posWidth in positions)
    {
        if (i != 0)
        {
            //if not at the last one
            if (i < positions.Count - 1)
            {
                Vector2 offset = SliceMath.normalOneSide(prevPos, posWidth.position);
                offset.Normalize();
                float xOffset = (offset.X * i * posWidth.width);
                float yOffset = (offset.Y * i * posWidth.width);
                vertices[currentV].Position = SliceMath.setVector3(vertices[currentV].Position, posWidth.position.X - xOffset, posWidth.position.Y - yOffset);
                vertices[currentV + 1].Position = SliceMath.setVector3(vertices[currentV + 1].Position, posWidth.position.X + xOffset, posWidth.position.Y + yOffset);
                currentV += 2;
            }
            else
            {
                //set the head
                Vector2 length = (posWidth.position - prevPos);
                length.Normalize();
                float xOffset = length.X * posWidth.width * headSize;
                float yOffset = length.Y * posWidth.width * headSize;
                vertices[currentV].Position = SliceMath.setVector3(vertices[currentV].Position, posWidth.position.X + xOffset, posWidth.position.Y + yOffset);
            }
        }
        prevPos = posWidth.position;
        ++i;
        posWidth.update(gameTime);
    }
}