Harry James potter was beginning to get desperate. He had finally destroyed all of tom's horcrux and he had gone to face him just like he and Dumbledore had planned, unfortunately he had forgotten something. While it is all good to say that you will face a monster without killing it yourself it has never actually worked. So while he may have the elder wand and be the master of the deathly hallows he was still fighting against a powerful wizard many times his age. Now this did not leave him defenseless as most people would think. or there is one thing that the deathly hallows allow their master to do, as otherwise it is impossible, no matter who you are.
The deathly hallows do not, like was believed, master death. Nothing can, it is simply a facet of the universe. No what the deathly hallows allowed their wielder to do was control dark energy. This would seem to not be much at all however it has been theorized by wizards ever since they discovered it that if someone could control it they could potentially do anything.
However while this was true up to a point, Harry had had no time to prepare or train before this battle so the most he could do is throw gobs of the stuff at old moldy and hope for the best. Now after a while f sitting behind the Whomping Willow to rest for a while harry eventually decided to just do what he could and hope for the best as at this moment he really couldn't think of much that he could do. So in a sudden fit of either incredible stupidity he stood up from his hiding place and started looking for his inhuman enemy. Upon finding him he noticed that he was in the middle of casting the avada kadavra at him so he quickly brought up the elder wand and sent out a bolt of as much dark energy as he could and jumped back. Now when the two bolts connected there was no sudden backlash of the killing curse nor spectacular light show. the bolt of black light from harry just seemed to swallow the curse whole as it continued on its way.
Voldy upon having seen HIS spell be swallowed by whatever it was Potter had done was rather surprised, after all if you had just fired a supposed unblockable weapon at your enemy you would naturally expect them to be the one to die, would you not. So while he was frozen in his stupor. Harry's bolt had finally reached him. Upon hitting Tom there was nothing for a moment before quite suddenly his skin peeled off, his muscles liquefied, his organs pulped, and his bones became so much mush.
After having seen this everyone was rather stunned. and after a while most ended up messing on their shoes, and then throwing their wands down while begging to be kept away from potter. Hence in a stunning display of brutality that not even Voldemort would have thought to issue Tom Marvolo Riddle was finally dead and the war he had started was over.
In the end harry went on to live quite happily. He had three children with his wife Luna Lovegood, a boy and two girls, find his wife her crumple horned snorkack, and was the only ever user of dark energy.