x(x5-1+y(4+3y))+y-2 is one way to regroup, but it doesn't help to factorise.
However:
When y=0, x6-x-2=(x+1)(x5-x4+x3-x2+x-2);
when y=-1, x6-2x-3=(x+1)(x5-x4+x3-x2+x-3);
when y=-2, x6+3x-4=(x-1)(x5+x4+x3+x2+x+4).
Other values of y do not produce a polynomial with rational factors. But:
When y=x, x6+3x3+4x2-2=(x+1)(x5-x4+x3+2x2+2x-2).