Professor Dumbledore cast one last look over his shoulder at the doorstep of 4 Privet Drive. The hope of the Wizarding World, the Slayer of Darkness, the Boy Who Lived sat in a basket there, a letter explaining why he was there to be tended by his relatives. Everything he'd looked into, researched, planned, and prepared for said this was the right call, that this is what would lead to the boy growing into the type of young man the Wizarding World desperately needed in order to drive back the Dark Lord when he inevitably returned. He'd long ago accepted the concept of 'necessary evil', and knew just how rough it would be for the young Potter, growing up with his magic hating relatives...but it was necessary.
With that last bit of uncertainty, the Headmaster of Hogwarts turned his back and Apparated away, leaving no trace that anything magical had happened on that street on that night, leaving only the child - protected by charms to ensure his well being - waited to be discovered by his family, when the charms that would hide him from his enemies would activate, renewed once a year when he rejoined his family.
This sequence of events was most familiar to the multiverse, as it had played out any number of times. Young Harry Potter would grow up with the Dursleys, the pain of that life variable depending on how dark that particular branch of the timeline grew, and what events had slipped in before or after depending. Either way, the young Potter would grow up unaware of magic, only to be enraptured when he discovered it and caught up in the conflicts and miracles thereof. In any number of timelines, Dumbledore's plan would carry out - as far as it went - and the name of Harry Potter would again become a Hero to the Wizarding World.
...this is not one of those timelines.
Not long after the Headmaster had vanished, a squat bald man in a long coat toddled along the street, his limbs a bit stiff with the cold of the night. He swayed back and forth with his steps, his bulging eyes spinning with or without the turning of his head as he took in everything in his surroundings, enjoying a night unlike any other. A great evil had been cast from the Darkness, and all his kind were eagerly enjoying the cleansing of their home. As he walked, though, his eyes locked on the basket. "What's this?" he asked, his voice a little gravelly as he staggered up to the doorstep. Leaning over, he saw the infant inside. "Who'd leave a baby all alone on this night of all nights? That's just asking for someone - or something - to snatch him up for something unsavory." He leaned in closer, then paused and took a sniff. "Hmm...someone's careful, though."
His eyes twisted and locked onto the lightning bolt scar just under his hair. "What's this?" Reaching forward, he pressed his finger to the scar, pulling it back as he felt the energy there. He took a sniff of his finger, and his eyes widened. "Could it be?" He placed the tip of his finger against his tongue. "It is! This boy's been touched by death...and conquered it! So young, too? How could this be?" His eyes spun to spot the letter. Curious, he slipped a long nail under the seal and easily opened the envelope without breaking it. Pulling out the parchment, he perused it.
As he read, his bulging eyes widened, and his mouth slowly split into an almost terrifying grin. "So you purged the evil from the Darkness, did you lad?" he asked in pleased surprise. "At your age, that's impressive!" He frowned as he caught sight of the name of the evil. "Even if he weren't evil, no one who Runs From Death belongs in the Darkness. And now his followers want you dead?" His grin returned as he chuckled, sitting down next to the basket even as the young lad's eyes opened, staring up at him in surprise...but with no fear. "Well, now I know why you've been left here! A start like that, you belong with your clan, blood or no blood!"
Scooping the boy out of the basket, he held him up carefully as he grinned up at him. "And there's no doubt about it my boy. You...are an Addams!" As he declared that, lightning flashed out of the cloudless sky, thunder boomed...and the boy grinned from ear to ear before leaning forward to try and eat the man's thumb despite the lack of teeth. Chuckling, the old man pulled out a bone of some sort and stuck it in Harry's mouth to suck on. The smokey flavor of the reptilian phalange immediately caught his attention, and he grabbed hold of it with both hands and sucked.
"That's a good lad!" the man declared happily as he shifted some of what he was carrying into the basket before slinging it across his back, nestling the young boy into the crook of his arm. "Course, an Addams needs a father and a mother to grow up right. Hmm...my brother did say he and Morticia were trying for children." He grinned down at the baby in his arm. "Come along with Uncle Fester young lad. It's time to go home."
With that said, Fester Addams set off in the one direction every Addams instinctively knew to go, the knowledge in their very blood whether they were born of the clan or brought into it because they belonged...the way home.