5000 year War

The 5000 Year war began when Matt Final Orion gave Shaggy his Cosmic Form for the sole purpose of destroying the abyss. The Battle lasted over 4600 years before the defeat of the allies.

Planning
Shaggy new that if he was going to stand any chance of winning he would need help. He walked around the entire Gigaverse for like 200 years, convincing army's to aid in the assault. After that Shaggy and generals from each army devised a plan so fucking crazy that it like could actually have worked.

The plan involved the Armys going under the abyss and flipping it upside down. The Theory was that when they did this gravity would get all fucked up and like the abyss would be all fucked up.Really they just assumed the outcome would be bad for the abyss.

The Flipping
On 3465 (Normal World time) Almost all of the allied forces stealthed their way under the abyss and lifted really hard, surprisingly it actually fucking worked and they flipped the abyss completely up side down.

Scientists believe that when the universe flipped, all of the gravity was inverted and pretty much everyone inside fucking died. Since it was the abyss however in 2.32450235235 seconds all of them came back fully adjusted to the new environment.

The Battle
Because of the whole flipping thing like the entire abyss got really pissed off and flooded out like a bunch of bees (ouch), and with that the fighting began. literally like 20,000,000 Proto soldiers instantly began pushing hard into the abyss, the EDF called in 28 Genocide guns to sweep the outer abyss, and Shaggy with his group of extremely powerful gigaverse leaders (such as El Proto Blanco and Vape God Gru) dove deep into the abyss.

While the Battle was raging on Vape God Gru used toxic mist and killed around 400,000 abyss spawn in one turn. Shortly after Cosmic shaggy froze the 5th dimension and performed a multi dimensional soul crush on around 50,000,000 of the abyss's forces, which ended up being half of the casualties for the abyss.