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