While Chomper is out in the Mysterious Beyond looking to teach its sharptooth inhabitants to be "nice", he walks into a cave to rest, and is confronted by the fastbiter trio. After a botched attempt at talking to them, they snarl at the young tyrannosaur and pursue him out of the cave.
During the chase, Chomper gives the red raptor the slip by going under a log too low to the ground for them to follow; immediately afterwards, the green and purple raptors crashing into their partner.
Later, the four theropods come to the edge of a cliff by a river; Chomper, a ways ahead of the fastbiters and out of sight, throws a rock to distract them, coaxing them to a steep slope and making them fall into the rapids below. They are not seen again afterwards, and it is unknown whether or not they drowned in the river or survived the ordeal.
- The green Fast Biter look similar to Thud, one of Red Claw's subordinates, except that this Fast Biter's green color is more dull.
- It is unknown as to why the Fast Biters didn't understand Chomper when he spoke in Sharptooth language. They were possibly hungry and were following their predatory instincts.
- Incidentally, these three Fast Biters have the same coloring as the sharpteeth from The Land Before Time X: The Great Longneck Migration.