Grundles

The Grundle (also known as a Dromaeosaurid Theropod Grundalicus) is a reptilian predator that roamed Ninjago in prehistoric times. By the time of the cartoon series, its species was long extinct, with a skeleton on display in the Ninjago Museum of History.

Its first (and so far only) appearance was in "Child's Play".

History
Lord Garmadon attempted to resurrect the Grundle with the power of the Mega Weapon, seeking to use it as the ultimate anti-Ninja weapon. The Ninja interfered with the ritual, causing them to be reverted to children - unfortunately for them, the Grundle was still revived and began stalking the city in search of its prey.

With their fighting skills reduced with their age, the Ninja were helpless against the Grundle, but Lloyd took them to Rufus MacAllister's comic book store, where he felt that they could find some defense against the beast. Using light-up illumaswords, the Ninja were able to keep the Grundle at bay for a time, but the prehistoric monster eventually knocked the weapons from their hands.

The Ninja were only saved by the arrival of Nya and Sensei Wu, who had brought age-increasing Tomorrow's Tea with them. Despite being in range of the tea's effect, Lloyd threw the tea at the Grundle, undoing the time-reversal spell that had revived it and de-aged the Ninja. The Grundle collapsed into a pile of bones once again, and the Ninja were restored to their former selves - along with Lloyd, who was now a young adult.

Abilities and Attributes
The Grundle is fast, powerful, and resilient, having a hide immune to ordinary weapons. However, it is a nocturnal creature, and thus very vulnerable to light - even the relatively meager light projected by toy illumaswords is enough to make it flinch.

Its claws can tear through metal and its senses are keen enough to track even a ninja. It has some degree of poison dripping from glands behind the teeth, but it is unknown how potent it is or what effects it has.