I think Mangala's best game for us was against Chelsea last season, he kept that dirty, cheating gobshite quiet for the whole game.
I actually think he's better than Otamendi, who still just dives in and spends too much time sat on his arse as yet another forward takes the ball past him.
My dad tells me of a player of whom it was said "Either the ball gets past him, or the man, but never both together." That's the kind of centre back we need, especially to deal with pricks like Costa. Stand up to him, niggle at him, stand on his toes at corners, whisper things about his mum or his mrs to him, he'll get himself sent off sooner rather than later, easy.