RECOVERY OF POSSESSION

The application and the suit becomes infructous.  The plaintiff may withdraw the suit with liberty to file a fresh suit for cancellation of the sale deed made by the defendant in favour of X.

Depends when the transfer took place.

If during pendency then the transfer is subject to decree, so you can continue with the present suit adding the purchaser as party defendant. Additionally if there was a restraint order, you could move an application U/r XXXIX R 2A for disobedience

If before the suit, then a fresh suit with the following relieves:

1. Declaration to the effect that ptf is entitled to possession (or for a declaration of his rights);
2. cancellation of the transfer/sale;
3. direction to put the ptf in possession

In the latter case you may have to array the purchaser & Registering office as party defendant

 I follow what Mr. TVD Rajkumar has stated, If the transfer took place during the pendency and after filing of suit the Plaintiff has to move an application under Order 6 Rule 17 for amendment of plaint and impleadment of purchaser as a party 

The remedies are:-

1. Implead purchaser as party to the suit, in present suit.
2. Amend the plaint and seek declaration of title,permanent injunction besides posssession and also assail the sale deed.
3. File fresh application for stay against purchaser to restrain further transfer.
4. Seeing the WS of purchaser,fresh amendment of pleadings and relief in the suit may be sought.
5. If the transfer was effectuated during pendency of the suit,file application under order 39 rule 2A as well as Application for Mandatory Injunction seeking back/ delivery of possession as an interim relief.

              I hope this solves your problem.