NEVER underestimate a Mal'damba, he is the best dueling suport if the game, even as a flank be wary of his reload, never take on Mal'danba at close range alone, if you can avoid it.
Don't engage enemy tank, if Mal'damba is near him. While you fighting frontliner Mal'damba have time to aim his Cobra Toss.
Attack Mal'damba if he separated from his teammates. It is difficult to aim "Cobra Toss" while under pressure.
When ulting as Mal'damba be careful of shields and the cart, both of those can stop your ult from being as effective as possible by blocking it from hitting anyone. Try and make your ult detonate above the cart.