During his wars with the Koopa Kingdom, Evil Link briefly seized Roy Koopa's hotel and plundered Roy's vast toaster hoard. After Link died in 2040, his successors tried to appease the Hylian populace by letting them take Link's personal wealth, including the toasters. Soon, people all around Hyrule were using Link's toasters. Unknown to all but a few high-ranking Koopas, Ludwig von Koopa, expecting the hotel to be taken, had planted tiny, remote-detonated packs of highly-radioactive hylium in the wiring of all the toasters. By the early 2060s, Hyrule had lost all the territory it gained during Link's reign and entered an economic depression. Looking for a new source of resources, Birdo and her advisors decided to invade the former Mushroom Kingdom, now the Mushroom Republic, in February 2068.
The Koopas, allied with the Mushrooms since Princess Toadstool was overthrown, quickly issued a warning to Hyrule that if they did not withdraw their forces from Plit within a month, they would activate an unspecified "secret weapon." The Hylians refused to comply, so on March 5, 2068, toasters throughout Hyrule exploded, spilling radiation everywhere. Over nine million Hylians were immediately affected by the leaking radiation, and winds quickly carried it to all but the most remote and mountainous areas of Hyrule. One experimental nuclear reactor in the Koridonian desert happened to use toaster wiring due to lack of funding; this caused the place to explode, killing everyone within a forty-mile radius and rendering a good portion of Koridon and Gamelai uninhabitable.
Needless to say, it would be a long time before Hyrule dared to go to war on Plit again. More importantly, the gene pool of Hyrule was radically altered; most Hylian births over the following years produced only mutated forms. In accordance with the peace treaty that had ended the Form Wars, these newborns were sent to Truceland. Of course, these forms' parents didn't like this at all, and unrest in the form of protests, riots, and boycotts threatened the stability of Hyrule. People also began to call the Hylian leadership hypocrites for allowing a form, Gay Luigi, to serve in the government. Finally, in 2080, Birdo signed the Form Acceptance, Rehabilitation, and Integration Act into law, effectively ending the exile of forms to Truceland. The irradiated areas in Gamelai would later be settled by Gay Luigi clones, and in 2155, Hyrule recognized these territories as the sovereign state of Gayland.
An unidentified individual from the future once sent a message to the early 21st century to warn about various coming disasters, including the Toast Meltdown. The message ended up in the hands of Fat Mario and Gay Luigi, who decided to use a time machine to try and change future history. Mario and Luigi got to the Toast Meltdown last, and Mario even tried fatally electrocuting himself to disable the radioactive toasters. However, the Time Travel Police ultimately intervened, destroying the message from the future and erasing Mario and Luigi's memories of their quest. Despite this, WalrusGuy somehow heard about the event and adapted it into the YouTube Poop series Mario and Luigi Travel Through Time.