Viktor Krum is Seeker for the Bulgarian National Quidditch Team and Durmstrang's champion for the Tri-Wizard Tournament.

Harry's first task is to collect the golden egg from a Hungarian Horntail Dragon. Charlie Weasley describes the Horntail as a "vicious thing" whose "back end's as dangerous as its front" because its tail has spikes protruding every few inches.

Rita Skeeter is an unregistered animagus that turns into a beetle. She uses her ability to eavesdrop on private conversations to come up with sensational stories for the Daily Prophet.

After Harry faints when a Dementor approaches him on the Hogwarts Express, Professor Lupin gives him a large piece of chocolate which makes him feel better.

Harry and Cedric decide to end the Tri-Wizard Tournament in a tie by taking the Tri-wizard Cup together. The cup is actually a portkey, which Voldemort uses to bring Harry to him. When Harry and Cedric both appear, Voldemort has Cedric killed.

A bezoar is "a stone taken from the stomach of a goat, which will protect from most poisons." Harry saves Ron from being poisoned by shoving a bezoar down his throat.

Dolores Umbridge is brought in by the Ministry of Magic as the Fifth Year Defense Against the Dark Arts teacher to convince the students that Voldemort has not returned and there is no reason to teach defensive magic.

A thestral is a horse-like creature, with a dragonish head and black leathery wings. They are used to pull the carriages at Hogwarts and are only visible to someone that has experienced death.

A curse was placed on Marvolo Gaunt's ring, which Voldemort was using as a Horcrux. The curse was designed to kill anyone who wore the ring, but Snape managed to temporarily contain the curse to Dumbledore's hand.

When Dumbledore visits Horace Slughorn to try to convince him to be the new Potions professor, Slughorn pretends to be an overturned armchair in his apparently ransacked house to try to convince Dumbledore that he is not home.