You can treat the original as lost. Make a complaint to local police station with regard to loss of patta, after that publish a notice  in local news paper warning the general public, banks not to deal with anyone claiming possession of original also offer handsome reward to finder of patta. This will alert him and he may come for settlement on your terms. Otherwise you can proceed with deal with land with all proof of complaint the public notification.

It is better to engage an experienced lawyer. 

no registered sand deed has been executed in his name 

2) purchaser does not have clear and marketable title to property 

3) he has only possession of land 

4) purchaser has to file suit for specific performance to direct your mother to execute registered sale deed in his favour 

A patta is by itself not a document to title, as it cannot confer title upon someone. It is a Revenue record evidencing title. Please find out with whom the original sale deed, gift deed or partition deed conveying the title to your mother or to you is. By merely being in possession of the patta, X cannot legally claim title. However, there is a risk of his doing so by claiming adverse possession if he has been in uninterrupted possession and enjoyment of the property for 12 years or more.

You can settle with him or dispute the same and deny the sale by approaching court. 

Sir, If you need any further assistance.You can approach me through Kaanoon or LinkedIn.

You don't have to beg him 

If he is not agreeing for any terms, ask him to proceed legally.

In the meantime you may submit a complaint to the police stating that yo have lost the patta after which you can apply for new patta from the revenue department.

The patta in his possession shall not confer rights to him over the property in any manner.

He knows the background facts, hence he is still hesitating to take any legal action.

Besides in the absence of any sale agreement between you both, he cannot claim or file a suit for specific performance of contract too.

If the money given by him was more than three years ago, you may not have to worry bout it because it is barred by limitation, hence do not commit anything about it because it would give a fresh lease of life from the date of you acknowledging the amount obtained from him.

- A Patta is a legal document issued by the Government in the name of the actual owner of a particular plot of land. 

- Further, only having the property documents cannot make a person legal owner of any property , and for transferring the Patta , a title deed is required .

- If he not agree for paying more than the market price , then you can send him a legal notice for cancelling the deal if any . 

- Further , as no agreement was executed by your mother , then cannot even file any case against her legally. 

- Further, as the patta is in your name , then you can publish a lost advertisement in the paper , and get the certified copy from the competent authority . 

- Further , if he is in possession of the property , then you can file a suit for evicting him .

You can contact me , if further more suggestion needed in this regard. 

A patta is merely a revenue record at the end of the day and by no means any proof of conferring title whatsoever. Other than that, he can claim adverse possession of the property if he has been in possession of the property for more than 12 years but even in suit relating to that, he would have to show his title to the property failing which he will be adjudged a trespasser only. So, since you are saying there is o registered sale deed yet, you can deem the transaction to have not taken place at all. Further, make a complaint to the police you have lost the patta and attaching that complaint as an annexure make an application to the revenue authorities to issue new patta based on your title to the property.