\[\left( - \frac{1}{8}x^{2}y^{3} \right) \cdot \left( 2x^{6}y \right)^{4} =\]
\[= - \frac{1}{8}x^{2}y^{3} \cdot 16x^{24}y^{4} = - 2x^{26}y^{7}.\]