We can all see clearly for ourselves what Zaib is doing to Kripa... as Nittu di said, he's going to destroy her defenses one by one, eliminate her pillars of support and finally destroy and mutilate her soul. He's going to give her a bit of what he had to go through...
Kripa was safe in the illusion that she had left angad far behind in some hidden abyss of her memory... she enshrouded herself in this false security, only to further expose herself to Angad's memories - making herself more vulnerable to Zaib's attack. I am pretty sure, that her marriage to Prithvi was a blow to her own soul, which is synonymous with Angad... because her heart and soul are still deeply bonded with Angad and the memory of him.
Angad's idea is to make Kripa suffer as much as possible... bit by bit... slash open old wounds and never let them heal. And so, he arrived in the form of Zaib, Kripa's satan, and Angad's angel of deliverance. Zaib is just a mechanical revenge machine, driven and fuelled by Kripa's betrayal and open distrust of his love. What must have been incredibly soothing to his injured soul was probably the look on Kripa's face when he first appeared before her in this new avatar called Zaib.
It's like rebirth. Only now, what was once the light of Angad's life is now the object of intense hatred for Zaib. Zaib's goal is Kripa's destruction and he will take his time: tormenting her with the knowledge that he shares the same face that Kripa placed her love upon.
The wheels are in motion. The pawns have been laid out on the chess board. And now ensues a battle: the battle to avenge Angad's pain and abandonment. Zaib's strategy is simple, but ultimately , he takes a complicated path to the goal. He will eliminate each of Kripa's pawns with incredible ease and prove to her that he is a force to reckon with. His sneering sarcasm and stabbing needles will splinter Kripa's heart into a million bleeding pieces...
He will storm into her already chequered battlefield of a life with the force of a hell sent battering ram, shatter her defences and expose her to his raw fury...
the game has just begun...