Prepare a Latias. If your friend knows competitive playing, he will expect Calm Mind once, and will demolish it with Tospy-Turvy. You, instead, use Draco Meteor .He will give you a + sp.atk for free.
Alternatively, prepare a Taunt user, or a Scizor. Use Bug Bite or any Bug move and Malamar is an old story. You can also use Magic Bounce (not sure if this works) to bounce back the changes.
Shortly, you have 3 solutions:
- Defeat Malamar quickly with a bug
- Use own status-reducing moves like Overheat or Close Combat to gain an advantage for the rest of the battle.
I recommend the third option, with Scizor:
Scizor @ Scizorite:
EVs: 220 Atk / 36 HP / 252 Def
- Superpower (Third option)
- Bug Bite (Second option)
- Bullet Punch
- Roost / Aerial Ace
Or any Pokémon that you think able to do it.