Nagini

Nagini is Lord Voldemort's huge pet female rattlesnake.

Goblet
Nagini is first seen slithering up the stairs of the Riddle House, old home of Tom Riddle. Nagini rises from behind a milkman who is spying on Voldemort and Wormtail, and scares him, before the Dark Lord kills the milkman.

Hallows
When Harry and Hermione visit Godric's Hollow looking for Horcruxes, Nagini possesses the long-dead corpse of Bathilda Bagsho

agini, in Bathilda's body, finds Harry and Hermione and lure them to Bathilda's house. Hermione and Harry notice her odd behaviour. Nagini then bursts out of Bathilda's body and attacks them. A battle ensues at Bathilda's house, and Harry and Hermione magically throws things at Nagini, who starts shooting poison at them. When a lamp is hurled is her mouth, Nagini unintentionally swallows it and Hermione uses 'Wingardium Leviosa' on the lamp inside Nagini, throwing her down the stairs. But just as they think she's gone, she gets back up. Hermione blasts a spell at her, and Disapparate. However, Harry's wand is broken in the progress...