What Malzahar needs is a nerf to his broken passive
Increasing the mana costs won't do nothing to him. He needs a nerf to his passive and the Voidling damage to monsters from 75% to 50%.
His passive is so incredibly broken, if you try to burst him out, he will soak up all the damage for 1 second because of his retarded 90% damage reduction.
If an assassin tries to go kill him, he will just use all your combos on you and your dead. 1 second is all assassins need to kill someone, but his passive completely nulifies the damage.
Either have a Banshee's passive for 1 ONLY CC instead of 1 second CC block or reduce the damage reduction, because it's too high.