Joker Teeth

Joker Teeth are an item used by The Joker in Batman: Arkham Asylum, Batman: Arkham City, Batman: Arkham Origins Blackgate, and Batgirl: A Matter of Family. They are used to distract Batman through the levels of the game. The teeth play no major role in any of the three games: they just serve as part of The Riddler's Challenges, and are one of Joker's gadgets in "Play as The Joker" DLC in Arkham Asylum.

Arkham Origins Blackgate Incident
Twenty Joker Teeth are scattered all around the Administration portion of Blackgate Prison. Those teeth are armed with explosives, and blow up if they are either destroyed, or if Batman walks too close to them. If the player destroys them all, they are awarded with a trophy.

A Matter of Family Incident
The teeth appear again, and are scattered around Seagate Amusement Park. Destroying them all is a requirement for a trophy/achievement, as are Harley Quinn's Jack-in-a-boxes and Joker Balloons.

Arkham Asylum Incident
Joker uses the teeth to distract Batman through the story. They also serve as one of Riddler's Challenges. They can at times be heard yelling "Nya-nya-nyanyanya!" in Joker's voice. They are also one of Joker's gadgets in Predator in the DLC, "Play as The Joker", but much like the ones found in the Blackgate Incident, they are equipped with explosives.

Walking versions of the teeth are also used by Joker while he fights Batman upon injecting himself with Titan, and similar to the Predator Challenges as aforementioned, they also are equipped with explosives. When they get close to Batman, they start to jump up and down as well as make comical honking noises before they explode.

Arkham City Incident
Again, Joker uses the teeth to distract Batman, but instead of the teeth being spread across the whole map, they are only in two parts of it: the Sewers and the Subway.

Trivia

 * They also appear in the game Injustice: Gods Among Us as one of Joker's attacks.