Harry and Dudley Start Hogwarts

Uh oh... We're in trouble

"HARRY. Why do you have Voldemorts familiar around your neck?!" Lily asked, only to have a reasurring hand placed on her shouler by Sirius.

"It's Nagini, he has been looking for me, as I am one of the only people left in Wizarding Britain who can talk to snakes."

"The only one, don't put yourself down. You are worth far more than that."

"The only parsletounge left apparently, sonce Mouldy Voldy died. Sorry, nagini!"

"Either way, I'm not too sure about you having him in the house." Sirius mumbled.

"It isn't the snake that's bad, and she has a strong bonding ability, which means that she will equally listen to me, and she knows valuable informantion about Voldemort." Harry reasoned.

"Okay, you can keep her." Lily decided, making Harry smile and Sirius faint. 

The Grangers left half an hour later, and Hermione decided to research magical snakes and horcruxes, but that word wasn't said out loud near their parents!

The next day Harry and Dudley went to diagon alley with Ron and Sirius (and Nagini) and headed towards Gringotts. Harry wanted to know more about his inheritance. Lily potter said that any of the vaults he could take items from, however, he needed to be careful. 

At Gringotts, Hary re-did the blood tests, proving im to be the heir to the Potter estate (several vaults pass through male blood lines), all four founders (as above, female relations can access vaults in emergencies, but after the age of 11, male sons inherit the vault) and, most excitingly, the heir of Merlin. In all families, he was the last heir, and therefore, had a lot of power, and six seats on the Wizangamot when he became of age. Sirius had access to all of the black family vaults. They also discovered that he was a parsletounge (well, Sirius and Griphook discovered), an animagus, a metamorphmagus and part madge. Most of these powers had been blocked by the head of the wizengamot, but these blocks were removed on demand, and soon Harry was supporting blue hair with yellow streaks.

They arrived at the Slytherin vaults first, which consisted of many different vaults all linked together through a series of passages, which would be easy to get lost in if you weren't careful. Harry, within this one vault, had more Galloens than the entire Malfoy and Black family combined. There were books all over the place, heavily bound and out of print, Harry looked at them and put them in a bottomless bag that he had charmed. One of which was all about horcruxes. 

In the Ravenclaw vaults, there were various spells about Hogwarts, including a map of all 500 secret passages. Harry hid this and vowed to add it onto the marauders map. Sirius nearly cried. They found 7 and there were 500! Only 1.4%! It also had a few books about wand lore, which he put in the bag when Sirius wasn't looking, as he wanted it to remain secret.

The Griffindor and Hufflepuff vaults added several million Galleons to Harrys inheritance each, and added several books to his personal library. The Merlin vault had several layers within it, including a potions lab,  with gold, silver and platinum cauldrons, Adamantite and Mithril cauldrons, Adamantium and pure diamond swords. It also had bows and arrows with basalisk venom, basalisk skin clothing, and basalisk proof glasses. Harry retrived 5 pairs so his friends could have them so they could  be protected if a basalisk ever does happen to attack. As an afterthought, he retrived a diamond dagger and the matching sheath and waistband.

In the Black family vaults, there were multiple interesting items.

"Harry. Harry... pick up your dagger and stab that cup."

"Why? It's a little disrespectful..." Nagini hissed.

"It's a horcrux, Harry. Voldemort can come back if it is alive. He has lots of horcruxes." 

Harry followed Nagini's orders and stabbed the cup. A scream eminated from it, making them all hide in fear. 

"Harry, what was that?" Sirius asked, shaking.

"One of Voldemort's horcruxes."