\[- \left( - a^{2}b^{3}c^{4} \right)^{4} =\]
\[= - \left( ( - 1)^{4}\left( a^{2} \right)^{4}\left( b^{3} \right)^{4}\left( c^{4} \right)^{4} \right) =\]
\[= - \left( 1a^{8}b^{12}c^{16} \right) = - a^{8}b^{12}c^{16}.\]