Around 18 BBY, Clone Force 99, otherwise known as the Bad Batch, received a mission from Ciddarin Scaleback: to salvage the wreckage of a transport ship that had crashed on the planet Silla.
Following the Galactic Empire's devastating attack on Kamino, which resulted in the destruction of the Kaminoan cloning facilities and cities, the Empire initiated its own cloning program. This program, lacking the Kaminoans' scientific expertise, operated from a facility located within Mount Tantiss on the planet Wayland. Emperor Palpatine directed these cloning projects. Some months after the destruction of Kamino, the Empire successfully cloned a Zillo Beast using DNA obtained from the same creature that had previously attacked Coruscant several years prior. This juvenile clone was being transported to Mount Tantiss aboard an Imperial vessel from an undisclosed location. During transit, it escaped its containment, attacking the ship's crew. After severely damaging the ship, causing it to drop out of hyperspace, the Zillo Beast pursued a surviving Imperial clone commando through the corridors. As the commando prepared to defend himself with an electrostaff, the beast ambushed him, dragging him screaming into the ship's ceiling shafts, where he was killed and devoured. Subsequently, the ship crash-landed on Silla, with the crash being observed by villagers nearby.
Ciddarin Scaleback, an information broker, eventually learned about the crash site. She offered the Bad Batch a deal: scout the ship for valuable cargo in exchange for 50% of the profits. Despite their reluctance to work with Cid after she had previously betrayed them, they ultimately accepted the assignment. Meanwhile, Royce Hemlock, the doctor in charge of the Imperial facility on Mount Tantiss, discovered the fate of Transport 904 and dispatched a recovery team to retrieve the ship's cargo.
The Bad Batch arrived on Silla before the Imperials and began exploring the wreckage of Transport 904. As they moved through the destroyed ship, the clone mercenaries began to suspect that something was alive and hunting them. After further investigation, the juvenile Zillo Beast, which had survived the crash, ambushed the group. Following a short battle with the rogue clones, the beast fled the ship and headed towards a nearby village, intending to feed on its power grid. Hunter, the squad's leader, pursued the creature along with Wrecker aboard their ship, the Marauder, while Tech and Omega re-entered Transport 904 to gather more information about the beast. In the meantime, the juvenile creature reached the power grid and consumed its energy, rapidly transforming into its towering adult form.
At the same time, a fleet of Imperial Venator-class Star Destroyers appeared above Silla, deploying numerous LAAT/i gunships and V-wing starfighters. These ships quickly descended to the planet's surface, followed by a science vessel equipped with a NNJ-40 "Thunderbolt" long-range ion cannon. Upon spotting the Zillo Beast, the Imperials divided their forces. The V-wings destroyed the remains of Transport 904, while the LAAT/i gunships chased off the Bad Batch and contained the Zillo Beast. After incapacitating the Zillo Beast with the ion cannon, they captured it and placed it in stasis aboard the science vessel. The Bad Batch was forced to flee off-world after a brief aerial chase. Simultaneously, three Rho-class transport shuttles deployed clone commandos into the village near the battle, with orders to secure the area and round up any witnesses to the cloned Zillo Beast.
The Bad Batch managed to escape into hyperspace before the Imperials could destroy their ship, taking with them secret information extracted from Transport 904. After reviewing the data and discovering Palpatine's intentions to exploit the cloning technology acquired from Kamino for his own evil purposes, Hunter decided to send the information to Captain Rex, who was leading a small resistance movement against the Empire. Back on Silla, the Imperial clone commandos rounded up the villagers and transported them off-world to an unknown fate.