Tyrantrum is a bipedal, dinosaurian Pokémon that resembles a large theropod. It is predominantly brownish red with scaly patterns on its skin and scattered orange highlights on some scales and ridges. Tyrantrum's head is proportionately large with a blunt, ridged snout and powerful jaws. It has black around its eyes and a light gray lower jaw covered by a beard of white, primitive feathers. Several sharp teeth are visible in the lower jaw, while the upper jaw is lined with orange-tipped, tooth-like projections. Over its eyes is a row of five spikes resembling a crown. Around Tyrantrum's neck is a feathery white ruff that extends over its shoulders similar to a cape. Its underbelly is gray with white borders and there are two orange spikes near the tip of its long tail. Its small forelimbs have only two black-clawed digits each, but it has powerful hind legs with three black claws each. Plated, armor-like ridges cover its knees, back, and the top of its tail.
Before its extinction 100 million years ago, Tyrantrum was known to be vicious but had the presence of a magnificent king. Its powerful jaws, capable of shredding thick metal plates like a car, made it invincible. It is theorized that its original form was completely covered with a feather-like coat. Tyrantrum preys on Amaura.
