The question is somewhat academic since the devil would not engage in such a discussion or game-play with you. And in any case, in this day an age not many people believe in him anyway; (to his undoubted delight). They see him as a euphemism for evil rather than an actual living being, albeit in a spiritual sense.
The devil exists all right. We cannot possibly believe in God and not believe in the devil. But he is cunning in camouflaging his existence from a sophisticated modern world which does not know what to believe any more.
The devil will use your past and your future to ruin your present.
He will take an instance or an event from the past and let it prey within your mind weighing down your progress and enjoyment of life today. Say for example you have had a disagreement with someone in the past. Something serious that has hurt you badly and has been left unresolved. The devil will use such hurt to make you resent what has happened and perhaps withdraw any forgiveness you might have given. Or, if you have indeed forgiven, he will use such hurt to remind you that the other person has never sought, nor cared for, your forgiveness. This is particularly poignant if such a person has passed away and therefore there is no opportunity for reconciliation.
But you must remember this, such a person is now in another spiritual world and has seen the instance of disagreement in all its clarity. If indeed he has been in anyway remiss, this is now a matter between him and God; and has nothing to do with you. There is no profit in allowing the devil to torment you further. If, on the other hand, some blame is attributable to you, then admit it and seek forgiveness from God; and accept such forgiveness lovingly given. To do otherwise would allow the devil an opportunity to overcome you; for our regrets of the past are the toys he uses to suppress us.
As for the future, we all have our doubts, fears or concerns as to what will happen then. Be they worries about old age, sickness, or our fears for the safety or well-being of our loved ones. This too is fertile ground for the devil to manipulate and lead us astray from God our Creator; and to spoil our enjoyment of the present. Giving way to such fears is both playing poker with the devil and a great disservice to God Himself, since it betrays a lack of trust and faith in Him on our part.
Christ too was tempted and tormented by the devil many times. He overcame such attacks through prayer and strengthened faith in God His Father. Let that in itself be an example for us.
The devil will never show his poker hand, but rest assured he is holding at least six aces!