While dinosaurs always get the glory, I happen to love all prehistoric creatures especially Terror Birds.
There is something about being stalked and preyed upon by a giant, insane, carnivorous turkey that is both absurd, and terrifying. Then there is the fact that they are basically feathered dinosaurs that flourished in South America right up until the time it merged with North America. The land bridge brought other predators like saber-toothed cats and the reign of the Terror Bird came to an ignoble end.
They don't appear enough in fantasy fiction and rpgs for my likeing. D&D has one, and Pathfinder has the Axe-Beak, but when was the last time you saw one in an adventure supplement?
Type: Animal, prehistoric. Can be found solitary or in packs (D6). Any environment except Arctic.
Size: Human or larger
Stats: High strength, agility and endurance. Animal, predator intelligence.
Weapons and Armour: Beak (high damage), Kick (high damage), Head Butt (high damage). Wing rake (low damage). Hide provides moderate protection.
Min/Max: Very fast runners. May hunt in packs or have camouflaged plumage in dense jungles/woods.
TWERPS: Terror Birds
Beak +1 Hit 3 Damage.
Kick: +1 Hit. 2 Damage
Head Butt: -1 Hit. 4 Damage