Calm Mind could work, but it won't help him much vs anything that can resist Psychic (Darks, Metagross, Kecleon, other Psychics with good special defense). Toxic will help vs other Psychics, but not vs Steel and he won't last long enough vs Dark to make it matter. You may need to consider a psysical attack; HP Bug or Fighting would be useful, if that's what it has. Even with Bite, he's not too flash against Dark, so perhaps even something like Return or Swift?