Answer
$(x-y^2)(x^2+xy^2+y^4)$
Work Step by Step
Using $a^3+b^3=(a+b)(a^2-ab+b^2)$ or the factoring of the difference of 2 cubes, then,
\begin{array}{l}
x^3-y^6
\\=
[(x)+(-y^2)][(x)^2-(x)(-y^2)+(-y^2)^2]
\\=
(x-y^2)(x^2+xy^2+y^4)
.\end{array}