The Niffler is a magical beast with a long snout and a coat of black, fluffy fur. They are attracted to shiny things, which makes them wonderful for locating treasure, but that also meant that they could wreak havoc if kept (or set loose) indoors. Nifflers in general are usually harmless.

Students at Hogwarts School of Witchcraft and Wizardry learn about Nifflers in Care of Magical Creatures class, an elective that could be chosen in the third year of their education.

Nifflers are assigned to Curse-Breakers by the Gringotts Head Goblin to burrow underground in search of treasures hidden in cursed sites.

Nifflers are rodent-like creatures with a long snout similar to that of a platypus and a coat of black, fluffy fur. Native to Britain, they live in burrows as deep as twenty feet below ground, and females produced six to eight young in a single litter.

Nifflers have a pouch on their bellies which hold far more than at first seemed possible, like the effects of an Undetectable Extension Charm on a container.

Nifflers are gentle by nature and could even be affectionate towards their owners. However, they could destroy belongings looking for sparkly objects, and for that reason it was inadvisable to keep them as a house pet. It was also implied that they could turn vicious if provoked, as the second Niffler released into Dolores Umbridge's office apparently tried to take a chunk out of her leg.
Nifflers were kept by Goblins to burrow for treasure.

Newt Scamander owns a niffler, which escaped twice from his suitcase during his visit to New York in 1926 and tried to rob both the Steen National Bank and a jewel shop of numerous valuables. In 1927, the same niffler produced four offspring each in a different colour.

Silvanus Kettleburn was known to keep 12 of them, even when they had wrecked his house, boat and his favourite prosthetic leg.

Jacob's sibling could keep one in the Magical Creature Reserve, and borrowed Madam Rakepick's niffler to help with finding the third Cursed Vault. Her niffler was known to be very well behaved.

Merula Snyde enlarged one using the Engorgement Charm, making it more dangerous.

During the 1994-1995 school year, Rubeus Hagrid used them as part of the Fourth years Care of Magical Creatures class. Prior to class he hid Leprechaun gold in the earth in front of his hut. He paired each student with a Niffler and promised a prize to whoever found the most gold. Ron Weasley asked Rubeus Hagrid if they could buy these Nifflers as pets, and with knowledge, Hagrid said his mum wouldn't want one because they wreck houses, but this was not a definitive "no". This means there is a very good chance that wizards could purchase Nifflers. When Hagrid caught Gregory Goyle pocketing the gold, he explained that trying to steal it was pointless, as Leprechaun gold was worthless because it disappeared after a few hours. Ron's Niffler found the most gold, so Hagrid rewarded him with an extremely large slab of chocolate from Honeydukes.

During Dolores Umbridge's tenure as Headmistress of Hogwarts School of Witchcraft and Wizardry, Lee Jordan used the Levitation Charm to levitate two Nifflers through her office window to wreck the office. Umbridge blamed Hagrid for it, and that did not help him in the least during her Hogwarts High Inquisitor inspections.

Nifflers were among the threats to the Statute of Secrecy that the International Confederation of Wizards had to deal with in the 2010s.

Source: Wiki