Harry & Dudley flee an abusive Vernon - to Severus Snape. Severus finds a home for himself & the boys with dragons and hunt the Horcruxes from there. The dragons - especially one - become their allies. Tom R is VERY different.
— Summary on FanFiction.net
3 Slytherin Marauders is an in-progress AUHarry Potter fanfiction written by severusphoenix, found here.Petunia Dursley, Dudley Dursley, and Harry Potter leave 4 Privet Drive and - after Petunia recovers from being shot - take shelter on a dragon reserve, thanks to Severus Snape. With help from Lucius and Draco Malfoy, Rosmerta, Tom Riddle, ex-Auror Hugo Savage and a dragon named Yvane, they start hunting Voldemort's Horcruxes.
3 Slytherin Marauders provides examples of:
Abusive Parents: Vernon Dursley, like in canon. Unlike in canon, Petunia is not abusive.
The Bait: the Aurors have Lucius the "Death Eater traitor" spend a night in lockup in order to lure more Death Eaters out of the woodwork.
Bavarian Fire Drill: Draco throws a tantrum and Lucius demands the Ministry workers stop whatever they're doing and assist him so that Arthur Weasley can sneak in to find evidence that Rufus Scrimgeour and Dolores Umbridge are plotting to steal Harry away from his family.
Big "NO!": Tom when he's sorted into Gryffindor. Also, in a more dramatic example, Snape when Harry's name comes out of the Goblet of Fire.
Bitch in Sheep's Clothing: Dumbledore. He hides behind his "kindly old grandfather" persona but he dumped Harry at the Dursleys and paid Vernon to abuse him so he can later swoop in and "rescue" Harry and indoctrinate him so that he will gladly die for the greater good.
Bullying a Dragon: Literally, when a Death Eater attacks a dragon that has befriended Harry Potter-he got his Just Deserts though the dragon later complained that he gave her indigestion.
Byronic Hero: Snape snarks that Sirius is just a poor "misunderstood Byronic Hero."
Calvin Ball: Harry, Dudley and some friends play water polo with a frisbee and rules thought up as they go along.
Dating Catwoman: Lampshaded with Tom and Dora, with Dora being an Auror-in-Training and Tom who the Wizarding world knows hails from a "dark family" and unknown to the wizarding world is an alternate copy of Voldemort himself.
Good Is Not Dumb: Arthur Weasley thinks up a diversion that impresses Lucius Malfoy.
Grave Marking Scene: After venting about his abandonment issues Tom gets some closure and leaves flowers on his father's grave. Later when Voldemort stumbles across the flowers, he's greatly puzzled as to who would give that S.O.B. flowers.
Groin Attack: when her ex showed up and threatened Harry, Rosmerta hit him with a hex that would "tie his penis in a knot."
Happily Adopted: Harry, Tom, and Beth by Snape and Rosemerta. And Lucius and Petunia get married so Dudley and Draco become step-brothers, and after finding her they adopt Lucius's daughter Victoria as well.
Hero Syndrome: Dumbledore. He's engineering a catastrophe when he leaves Harry with the Dursleys so he can "save" him later.
Hold Your Hippogriffs: Tom remarks that a lecture in History of Magic "set the kneazle among the jarveys".
Hoist by His Own Petard: when Lucius covertly hexes Hermione Granger who is annoying him, Lucius accidentally hexed himself as well. Earlier Vernon gets himself killed via drunken roardrage.
I Want Grandkids: Voldemort begins making these plans soon after learning of Tom's existence.
Identical Grandson: Snape makes everyone (even Dumbledore) think that Tom Riddle is Voldemort's son to explain the resemblance.
Inferiority Superiority Complex: Lampshaded with Tom Riddle. When some of the Weasley clan meet Tom they assume him to be an arrogant, wealthy, pure-blood Jerk Ass. They're later informed that he grew up in an orphanage and is overcompensating.
Insistent Terminology: Dumbledore and other members of the Hogwarts staff often uses words like "pranks" and "schoolboy spirits" for what normal people know as "bullying."
Jerkass: Mad-Eye Moody, Vernon Dursley and Sirius Black.
Just Deserts: McNair learns too late why you don't meddle in the affairs of dragons...
Knight Templar: Albus Dumbledore he encouraged and paid for Vernon to abuse Harry in order to turn Harry into a weapon that would be completely loyal to him and would be okay with dying. Also Alice Longbottom and Neville has inherited these tendencies as well. And Rufus Scrimgeour.
Loophole Abuse: The Goblins inform Tom that he can't completely empty out Voldemort's Gringott's vaults... so they leave him a single Knut. Also fugitives can seek asylum at Gringott's because "Gringott's customers are allowed to count their gold for as long as they like."
Luke, You Are My Father: An exploited trope when Snape and Lucius pass off Tom as Voldemort's son. Later played straight when Lucius discovers Victoria, a little girl that bears an uncanny resemblence to him.
Orphanage of Fear: Where Tom grew up. Also Tom and Harry rescue Beth and Tori from one.
Papa Wolf: If you try and hurt Harry Snape will end you if Tom doesn't do it first.
Parental Abandonment: Tom has these issues with his muggle father because as far as he knows his father just abandoned his mother for no reason. He also realizes that because his other self killed his father years ago he'll probably never know the full story.
Pity the Kidnapper: after Voldemort possesses Lockhart, Lockhart begins driving Voldemort (more) insane.
Tabloid Melodrama: it seems the staff of the Daily Prophet has nothing better to do than stalk an 11-year old boy.
Talking to the Dead: Harry and Snape visits James and Lily's graves at Godrics Hollow. Later Tom resolves some of his emotional issues after he visits and vents at his father's grave.
Worthy Opponent: Lucius felt this way about Frank Longbottom.
You Are What You Hate: Voldemort who is a half-blood himself. Also Rufus Scrimgeour who is very suspicious of Slytherins is a graduate of Slytherin House.