\[ y''(x)+y(x)^3 y'(x)-y(x) y'(x) \sqrt {4 y'(x)+y(x)^4}=0 \] ✓ Mathematica : cpu = 0.153641 (sec), leaf count = 33
\[\left \{\left \{y(x)\to \sqrt {2} e^{c_1} \tan \left (2 \sqrt {2} e^{3 c_1} \left (c_2+x\right )\right )\right \}\right \}\]
✓ Maple : cpu = 0.281 (sec), leaf count = 35
\[ \left \{ y \left ( x \right ) ={\frac {1}{{\it \_C1}}\tan \left ( \left ( {{\it \_C1}}^{-2} \right ) ^{{\frac {3}{2}}} \left ( {\it \_C2}+x \right ) \right ) },y \left ( x \right ) ={\frac {1}{{\it \_C1}}\tanh \left ( \left ( {{\it \_C1}}^{-2} \right ) ^{{\frac {3}{2}}} \left ( {\it \_C2}+x \right ) \right ) } \right \} \]