There is no need to pray for the Devil,his fate is sealed God's word is a closed book.
He will be cast into the lake of fire,along with death and Hell.
Start praying for him you just may end up praying to him.
Revelation: 20. 10. And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever. 11. And I saw a great white throne, and him that sat on it, from whose face the earth and the heaven fled away; and there was found no place for them. 12. And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works. 13. And the sea gave up the dead which were in it; and death and hell delivered up the dead which were in them: and they were judged every man according to their works. 14. And death and hell were cast into the lake of fire. This is the second death. 15. And whosoever was not found written in the book of life was cast into the lake of fire.