Here's another potential Silly Pure Evil Candidate.
What's The Work and Who Is The Candidate
Thomas and the Magic Railroad is an 2000 live-action/Model series hybrid based on the TV show, Thomas the Tank Engine and Friends. It's about a lost engine, Lady, who has magic gold dust that can allow people to travel anywhere in between worlds. On the Island of Sodor, Diesel 10 had returned and wants to kill off the magical engine in order to kill all the steam engines. So it's up to Burnett Stone, Lily, Patch, Mr. Conductor, Junior Conductor, and Thomas the Tank Engine to stop Diesel 10 from killing Lady.
Diesel 10 is the main antagonist of the film. He is a BR Class 42 Warship based diesel locomotive with an additional rooftop clamshell bucket nicknamed "Pinchy".
What Makes Him Pure Evil?
Even before the events of the movie, Diesel 10 was known to be a very devious diesel engine who hated the steam engines. Everyone on Sodar feared him even. When he found out that Lady's existence is what kept the engines alive, he chased her and threatened to destroy her. This chase ended in her crashing and being put out of commission for a very long time. This cause Burnett Stone to become depressed (other then the death of his wife, Tasha) as he tried to fix her. It also started to cause Sodor, Shining Time, and the Magic Railway to lose energy and slowly dying.
Cut to the present day, Diesel 10 returns to Sodor, thundered pass Thomas, Annie/Clarabel, and Gordon, startling them and getting them covered in dust. He then makes a stop at Tidmouth Sheds to mocked Thomas and James. He then tells them that he returned to find and destroy Lady again. The next thing he does tell Splatter and Dodge, his two henchmen, that he will destroy Lady, which they weren't fond of. After they warn him about Mr. Conductor coming to Sodar, he yells at them that he can do whatever he wants and that he'll get him too. He then dumped sneezing powder around Tidmouth, and after Harold the Helicopter flies over them, the sneezing powder gets all over Thomas, Splatter, and Dodge.
During the night, Diesel 10 uses Pinchy cause damage to the under repair side of the sheds, waking up all the engines, and demands to Mr. Conductor to tell him where Lady is, even mocking him for losing all his gold dust. The next time we see him, he is hiding in a shed nearby Knapford Station where he overhears Thomas and Percy talking about the Magic Railway and the buffers that lead to it. He then leaves to tell Splatter and Dodge about his find and he intentions to kill Mr. Conductor and destroy the entire Magic Railway. Toby then distracts him by ringing his bell. He is about to go out to kill Toby, but Pinchy traps him and his minions under the sheds he was in.
When he returns, he grabs a helpless Mr. Conductor and threatens to drop him off the viaduct in ten seconds if he doesn't tell him where the magic buffers are. He also tells him that he and all the steam engines will be history after he destroyes Lady.
The next time we see him is when Junior landed on his roof. He pratically kidnaps him and taunts him for losing his beach bag. He then proceeds to take Junior to the smelter’s yard, where James is working at, and he stops suddenly, lauching Junior right on to James's roof. He then attempts to kill them both by forcing James to back up, which would've caused him to fall into the smelting pit. He would've succeeded if Junior hadn't used the last of Mr. Conductor gold dust.
He finally returns during the climax and he finally finds Lady. He then chases Thomas, Lady, and Burnett Stone in an attempt to kill them. He also mocks them the whole chase. He is finally defeated when he falls of viaduct and into a barge of sludge.
Mitigating Factors?
Well, it's worth pointing out that Thomas and the Magic Railroad is not canon to the show, since nothing from the film is referenced in the show, and the characters who do return in the show from the movie, are very different from their original counterpart. So, in short, this version of Diesel 10 is not the same one from the TV show.
Now, does he have any redeeming qualities?... No. For starters, he doesn't care for his minions, as he always yells at them and belittles them. He also referring to them as "Splodge" because he thinks he doesn't have time to say both of their names separatly. He enjoys calling the steam engines "puffballs". He also refers to Thomas and James as "cowardly, cranky, worn-out hunks of metal who couldn't hurt a fly." So he only cares about himself. His TV show counterpart at least treated the other diesels with some respect and honor and even has some on-and-off moments. Although he does complement and cares for his claw, Pinchy, there's nothing indicating that Pinchy is alive or sentient. Also, Pinchy is a part of his body. So, I guess you can say he cares about himself.
Now for some who think he relays on fridget horror, that couldn't be further from the truth. The film makes it very clear that if Lady is destroyed, the steam engines will all lose their life. Not only that, Sodor, Shining Time, and the Magic Railway will all be destroyed too. We see what the Magic Railway covered in leaves and after Lady is running again, it gets restored. We get a dream sequence from Mr. Conductor showing the amount of destruction that is caused from no more gold dust. And as Mr. Conductor is looking down from the viaduct, he says that his universe is starting to crumble. These basically confirm that killing Lady would've destroyed all universes.
Heinous Standard?
No point in sugar coating this, Diesel 10 is the heinous standard of the film. There are no villains in the film that even come close to him. He is easilly the most heinous villain in the entire film, and, to extent, the entire Thomas the Tank Engine and Friends as a whole as he's the only one to threaten to destroy Sodar and kill every engine, especially being only on to be a threat to multiple universes. He also has personal villainy with Burnett Stone due to being one of the reasons that Lady crashed. The only villain who comes close is P.T. Boomer, but he was a cut character so he doesn't count.
Is He Silly Enough?
The only thing to keep him from being a full on Straight Pure Evil is that he has a few comedic moments that detracts from his villainy. These moments include him hitting himself with Pinchy, knocking down a roof to the sheds in the scrapyard to hit Toby but getting the roof to fall onto him and Splatter and Dodge instead, telling Splatter and Dodge to stop being stupid by hitting a coal hopper, only to have the coal in it spilled all over him, causing James, Gorden, and Henry to laugh at him, and after his defeat when falling onto a barge filled with sludge, he says, "Uh. Oh well, nice time of the year for a cruise." and then laughs.
Now, is he taken seriously enough to be a Silly Pure Evil? I would say yes as everyone in-universe treat him as a serious threat, with all of the engines fearing him. He's isn't a complete joke as his crimes are also taken seriously by the narrative. He is taken the most serious during the final confrontation at the end of the film, where he is the most serious he has ever been in the film.
Verdict?
I’d say yes in my opinion.