The Battle of Malastare, one of the fiercest battles of the Clone Wars, took place on the planet Malastare. During the battle, the Confederacy of Independent Systems attempted to deplete the Galactic Republic's fuel supply by sending a massive army to conquer the world. The army was deactivated by a prototype electro-proton bomb that was designed by Republic scientist Sionver Boll. This opened up a large sinkhole that caused the Zillo Beast to awaken.
As the Separatists were about to take over the planet and seize the royal palace, Supreme Chancellor Sheev Palpatine ordered the use of an electro-proton bomb to deactivate the Separatists' droid army. Jedi Generals Anakin Skywalker and Mace Windu oversaw the battle.
In 21 BBY, after an extended period of battle, the Confederacy was on the verge of capturing Malastare, which would subsequently grant the Confederacy access to the fuel reserves on the planet. In response to the Separatist attack, Chancellor Palpatine authorized the Republic forces to use the electro-proton bomb, a superweapon designed by Republic scientist Sionver Boll that was capable of disabling armies of droids and vehicles within its electromagnetic blast radius. However, Windu had initially feared that the weapon could potentially affect the planet's ecosystem, but the pair eventually came to an agreement at the Chancellor's urging.
As the massive droid army, under the command of the T-series tactical droid TN-123, approached the plain near the royal palace, the droid gave the command to open fire and thousands of battle droids started to fire on the outnumbered Republic forces led by Captain CT-7567 "Rex" as he told his men to hold the droid forces off until the bomb dropped. As Rex and the 501st Legion took out a few battle droids, the Separatists launched several squadrons of Hyena-class Droid Bombers and Vulture-class droid starfighters to bomb the Republic's forces. RX-200 Falchion-class assault tanks, Dug rail guns, and Dug debris loaders shot down many of them, but this led to several All Terrain Tactical Enforcers being destroyed by crashing starfighters.
The Republic then sent out its BTL-B Y-wing starfighter/bombers escorted by ARC-170 Starfighters and V-19 Torrent starfighters. The hundreds of Armored Assault Tanks attempted to shoot them down, though they were unsuccessful. A group of Dug warriors riding Insectomorphs attempted to charge the enemy lines, but were quickly killed by several DSD1 dwarf spider droids. Meanwhile, the clone troopers managed to hold the line, despite heavy casualties.
The Y-wings finally reached the drop site and the bomb was released. The bomb initially created a large explosion that further grew into an even larger electromagnetic field that obliterated the whole army and caused all electronics to shut down.
After the bomb was initially detonated, a massive sinkhole formed and swallowed up several Republic vehicles and troopers. This also caused the Zillo Beast to awaken.