It's true that I have time to grind Guardian, but seriously, a, hmm, level 80 mr mime, with dark as second type, could finish my team in a second. Malamar and Inkay, the only genuine dark/psychic yet, are only weak to bug and fairy, both types that my team does not cover (well there's Mawile but no fairy moves yet if I recall correctly).
But the idea of grinding my Scolipede sounds good. Does it learn good but type moves? I haven't used the poor thing in ages...