Please note these are my own opinions and not based on the Thomas the tank engine wiki fandom
I did like how the producers Britt Allcroft & David Mitton were able to do a Halloween theme episode towards the end of season 2 before the Christmas theme episodes at the end of season 2. What I like about the episode was how Percy decided to play a trick on Thomas after telling him and Toby a ghost story that Thomas didn't believe after Percy was finished. In the end it was a nice way of doing Halloween themed episodes near the start of the Thomas and Friends TV series. Overall I did love this Halloween episode and it was a nice start to have a Halloween themed episode.
Season 3 episode 7: Thomas, Percy & the Dragon (US)
I did like how the producers Britt Allcroft & David Mitton were able to do a 2nd Halloween theme episode in the series overall after doing "Percy's Ghostly Trick" back in season 2 in season 3. What I liked about the episode was at the start, they did a little bit of a recap from "Percy Ghostly Trick" where Percy asking Thomas about his dream of Thomas seeing Percy as a ghost where Thomas denied the allegations. What made me laugh was that Thomas got back at Percy for scaring him with the ghostly trick that Percy played on him by scaring Percy with the dragon that he picked up from the harbor for Sir Topham Hatt.
With this episode, I like how they focus this Halloween themed episode around Henry by having Henry being spooked near the viaduct at night while working with Edward. As Henry approached the viaduct, they saw an amber light & a red jacket hung from tree branches and the spooky sight of a crossing gates closing by themselves before passing a disused station that had a spooky figure watching them pass by into the fog. Makes for a spooky night for a tale from Thomas and Friends.
Video Link => Season 5 Episode 11: Haunted Henry
With this episode, I like how they focus this Halloween themed episode around the engines after Edward told the other engines a ghost tale that caused Thomas to tease Percy. Afterward Thomas,Percy and Duck were sent to the smelters to pick up a special. What makes it even more spooky was Duck volunteer Thomas to pick up one more load at the request of the yard manager to get back at him for teasing Percy. I did like this along with episode 13th from season 6 that is also Halloween themed.
Video Link => Season 6 Episode 12: Scaredy Engine
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With this episode, I like how they focus this Halloween themed episode around Percy and a disused mine that was stated to be haunted. Like how they portrayed Percy being scared when seeing different parts of the mine mysteriously disappearing into the ground while collecting some box cars from Maithwaite station and again for another station. Even more spooky was seeing Percy being spooked after seeing a bunch of garden gnomes fall out of one of the trucks that caused Percy to run away from the mine.
Video Link => Season 6 Episode 13: Percy and the Haunted Mine
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With this episode, I like how they focus this Halloween themed episode and focus around the engines hurrying around to finished their jobs early but Thomas and Emily were sent to the Smelting yards where Arry and Bert played tricks on them that causes Thomas to be spooked by Emily who had a tarp fell down on her which in turn Thomas mistakes her as a ghost and be chased back to Tidmouth Shed along with Arry and Bert. As it turned out to be a trick played on both Thomas and Emily, Sir Topham Hatt makes Arry and Bert return to the Smelters to do Thomas and Emily's Jobs as punishment. I did like the atmosphere of the episode as it gave off a spooky feeling
Video Link => Season 8 Episode 21: Halloween
With this episode, I like how they focus this around Thomas and Diesel where Thomas gets covered in a flour power all over and scares Diesel who thinks that what he sees is Thomas's Ghost chasing him who gets back at Diesel for biffing oil tankers passed Thomas at the docks during Halloween night. With this spooky Halloween episode, it gives a spooky feel when watching the episode. The only downside with this episode, is that the episode release for the United States was November 27th and not October 31st like how the time frame is within the episode itself. Otherwise it was nice to have Halloween theme episodes within the classical series (between seasons 1-11).
Video Link => Season 9 Episode 26: Flour Power
With this episode, I like how they focus this around Percy and Jack & the Sodor Construction Company for this episode. Like how Percy and Alfie were working together on Halloween night where Kelly tells a scary tale to everyone but after Kelly finishes the tale, Monty and Max spooks Alfie and Percy when they get back to work. Then Max and Monty got spooked by Thomas who they believed was the one eye truck and everyone got a good laugh out of it.
Video Link => Jack & Sodor Construction Company: Percy's Scary Tale