Which Decepticon transforms into a giant purple mechanical dinosaur?

The Decepticon that transforms into a giant purple mechanical dinosaur is Trypticon.

Trypticon debuted as a 1986 Transformers toy and is one of the franchise’s enormous city-sized Decepticons. His dinosaur mode resembles a mechanical Tyrannosaurus rex, while his other major configurations include a Decepticon city and a battle station. That combination makes him more than simply a dinosaur-shaped robot: he is also a mobile fortress and headquarters.

In the original animated continuity, Trypticon was created by the Constructicons from a city. He is portrayed as a devastating but relatively dim-witted weapon, often contrasted with Metroplex, the Autobots’ similarly massive city-bot. The two become recurring rivals in the cartoon’s later stories.

A common mix-up is with the Dinobots, especially Grimlock, Slag, or Snarl. Those characters are Autobots, and their dinosaur forms are generally smaller individual combat modes. Trypticon is a Decepticon and is distinguished by his enormous scale, purple-heavy color scheme, and city transformation.