Anyway I am going to try the simplest fastest possible thing I can think of and test it to see if it will work:
def f(Z):
(x, y) = Z.coords()
return (y & M)
where M is a bit mask and is varied to create new kangaroos
They say this fastest pseudo-random generator that is any good:
XorshiftYou need few lines of code to vary the mask, why not do this instead?