According to Darthenshmirtz, he claims that he was the one who came up with the idea of creating the Death Star. He also claims that it was originally designed to be a nutcracker, but the Empire stole the idea and turned it into a space station. To prove that he's the better Sith than Darth Vader, Darthenshmirtz created the Sith-inator to increase his evilness and Force sensitivity, and turn his nemesis, Perry the Rebelpus, into a Sith. To do so, Darthenshmirtz goes around picking up trash or any objects that were personally touched by Vader, since they can pick enough Force for the Sith-inator to power up. Perry is then sent by the Rebellion to stop Darthenshmirtz from completing the -inator, but he ends up being trapped in carbonite. However, as Darthenshmirtz attempt to hit the trapped Perry with the Sith-inator, he accidentally hits Ferb, which resulted in him turning into a Sith. Darthenshmirtz then attempted to get more objects touched by Vader to power up his machine, but by the time he got back, Perry has escaped and engaged into a fight with him. While Darthenshmirtz was fighting Perry the Rebelpus, the Sith Ferb ends up engaging into a lightsaber battle with Phineas. During the fight, Darthenshmirtz accidentally ended up getting encased in carbonate. However, Phineas manages to destroy the Sith-inator, resulting Ferb to turn back to normal, allowing them and their friends to escape the Death Star. This also allowed Perry to take the trapped Darthenshmirtz with him aboard his personal YT-2400 so that he can take him into Rebel custody. However, after the Death Star has been destroyed, Darthenshmirtz manages to thaw out from his carbonite trap and taunts Perry as he escapes in one of the ships' escape pods, much to Perry's anger. However, as he escapes, Darthenshmirtz discovers that the escape pod is platypus-sized, much to his dismay.
Darthenshmirtz wears the same costume as Darth Vader except without the face mask.
The character of Darthenshmirtz is what lead Dan Povenmire to start the Star Wars crossover. Some time after work was done on "Mission Marvel", Dan heard that Disney bought Lucasfilm and began drawing Doof dressed as Darth Vader, and texted it to the head of Disney TV Animation saying, "I smell crossover!"
His name is a combination of "Doofenshmirtz" and "Darth", the title given to Sith lords.
According to a medical scanner in his song, Darthensmirtzs' Midi-chlorian count is 12 per cell, which compared to Midi-chlorian counts in Canon: is the absolute lowest Midi-chlorian count ever recorded, whereas even Non-Force sensitives like Han Solo have Midi-chlorian counts of about 2,500 per cell.
With the existence of Darth Vader and Darth Sidious in the special, Darthenshmirtz's existence, as well as his plan to create more Siths, would be considered a violation of the Sith Lords' "Rule of Two" which establishes that there can only be two members, meaning if this was canon he would have been eliminated.
Darthensmirtz's "Lair" is actually the Death Stars' abandoned recycling center, and due to low upkeep the blast doors leading into the "Lair" are malfunctioning and that repairs won't be done until Thursday, it was later fixed, possibly by Ferb as he was modifying the Sith-inator.
If this was canon, "Thursday" would not even exist as a Galactic Standard Week consisted of five days instead of seven, with the closest-sounding word to Thursday being "Taungsday": the 3rd day of the Standard Week.
Despite not being Force sensitive, Darthensmirtz owns a lightsaber, albeit he mixed it in with his camping supplies and has been carrying around his flashlight instead.
Prior to the Destruction of Alderaan, Darthensmirtzs' real estate timeshare on Alderaan was worth 10 times more than when he paid for it back in 6 BBY, unknowingly behind him the Death Star was in the process of firing on Alderaan, destroying the planet and instantly dropping the timeshare value instantly.
If this was canon, the knowledge of Alderaans' destruction would not be revealed instantly as the Galactic Empire held a firm grasp on the HoloNet to filter what information was released, it was only days after the Death Star was destroyed that information on the planets' destruction spread out among the public, the resulting aftermath -along with a lack of a decent cover story for explaining the planets destruction- became one of the Empires' biggest embarrassing mistakes as instead of spreading terror among dissidents: the Destruction of Alderaan caused entire star systems to break away from the Galactic Empire and declare neutrality or to completely join the Rebellion, along with the hundred thousands of surviving Alderaanians that were off-world to immediately join the Rebellion; including many Alderaanian imperial officers.