The problem with mankey is that he's so unflexible compared to mienfoo. All he can really do is choice scarf, and even mienfoo out-classes him sometimes in that respect, being much more able to switch in due to better bulk and regenerator and then mienfoo has a lot more other tricks up his sleeve like a bulky eviolite set, sub-pass, etc. and doesn't care about mankey's movepool as he gets great coverage with two moves anyway.
Anyway, here's the set I've been using in sand to surprisingly good effect.
Aron @eviolite
EVs:196 HP, 196 atk, 116 sp. def
Adamant, Rock Head
-Substitute
-Head Smash
-Iron Head
-Superpower
This counters murkrow so well which is mostly why it went on to my team but it's actually proven to be useful outside of beating murkrow and vullaby. The EVs let it easily take stuff like life orb murkrow's heatwave, taking barely 25% in the sand. Head smash seriously hurts everything that dares underestimate aron, making it very easy to predict a double switch seeing as the opponent will rarely have more than one thing that can take it. Iron head covers head smash quite well, hitting hippo and mienfoo neutrally, and superpower lets him pick off things like ferroseed or a weakened bronzor. Substitute is mostly a filler seeing as eq is pretty redundant though I may switch it out for magnet rise so he can try and stall out hippo and can't be revenged by drilbur.