Zillo Beast

The Zillo Beast, sometimes referred to simply as "The Beast", was a semi-sentient, reptilian species endemic to the planet Malastare. The Dugs believed this gargantuan creature to be extinct long before 21 BBY; during the Battle of Malastare, however, the last specimen alive was inadvertently unearthed by an electro-proton bomb used by the Galactic Republic.

Supreme Chancellor Sheev Palpatine sought to use the Zillo Beast's indestructible hide to aid the Grand Army of the Republic. Shortly after the creature was brought to Coruscant for study, however, it broke free from its restraints and rampaged through the capital. In the end, the Jedi and Republic army were left with no other choice but to kill the Zillo Beast using a powerful toxin, the same one that had compelled it to ravage Coruscant, but in larger doses. It was then revealed that, after the creature was killed, Palpatine ordered the Zillo beast be cloned.

Characteristics
The Zillo Beast was a gargantuan serpentlike creature with a lengthy whip-like tail. At 97 meters tall, the Zillo Beast towered over all species on its native planet of Malastare and was considered at the top of its food chain until its presumed extinction. Its tail contained eight sharp spikes, and the beast itself uniquely possessed a third arm protruding from its back.

Its heavy plated armor was invulnerable to explosions, blaster fire, and even lightsaber strikes. Jedi Knight Anakin Skywalker discovered that gaps in the creature's armored plates could be exploited to damage or stun the creature. On one such occasion, clone troopers were able to subdue the creature by using stun tanks aimed at the gaps in its armor to put the beast to sleep for transport to Coruscant.

While in captivity on Coruscant, Doctor Sionver Boll observed that the creature was possibly sentient. This deduction was reinforced by the creature's behavior towards Supreme Chancellor Palpatine. After breaking out of its containment facility, the creature terrorized the planet in an unsuccessful attempt to kill the Chancellor.

Behind the scenes
George Lucas felt the Zillo Beast would dislike Palpatine and chase him. Dave Filoni joked with Lucas that the Zillo Beast could sense Palpatine was a Sith Lord, and was trying to warn the Coruscanti.