  We introduce a class of rank-one transformations, which we call extremely
elevated staircase transformations. We prove that they are
measure-theoretically mixing and, for any $f : \mathbb{N} \to \mathbb{N}$ with
$f(n)/n$ increasing and $\sum 1/f(n) < \infty$, that there exists an extremely
elevated staircase with word complexity $p(n) = o(f(n))$. This improves the
previously lowest known complexity for mixing subshifts, resolving a conjecture
of Ferenczi.
