Thomas the Tank Engine & Friends: The Lost Episode from 1996 (SuperMalechi's version)

This is known by BJ (from Barney & Friends) in June 7, 1999.

Prologue
BJ tells the prologue:

Several years ago, I bought and received a job lot of early Thomas & Friends videos and the like from an eBay seller, with the help of my friends Barney, Baby Bop and Riff. The auction's description mentioned that several of the videos were actually given to him prior to the release of the series on VHS, implying that the seller originally worked on the show in some way. Some of the early tapes he sent me were in relatively good condition (considering they're almost 3-15 years old) and some are a little worse for wear, with missing boxes, labels, etc.

Some of the tapes had the original labels missing and had crudely-written replacement labels stuck to them. Other tapes had earlier versions of certain episodes with extra (or missing) sound effects, as well as short bits of footage that did not make it to the final versions of the episodes.

The video that grabbed my interest the most, however, was a video simply called "The Lost Episode from 1996", which I believe was filmed in 1996, before the rest of the 4th season episodes in 1996-1998.

Video
Intrigued, I played the video before any of the others I received in the Job lot.

The video starts with a date displayed in the bottom right hand corner. It only appears for a few seconds, and it says "5/2/1996" which would mean the 5th Feburary, 1996. According to most sources, 1996 is the year which more Season 4 episodes are made that year.

After this, the 1996 version of the Thomas & Friends Season 4 intro plays regularly. When the title card appears, it says "Seventeen's Worst Day".

Michael Angelis narrates this episode, and merely sound effects, making it all the more unnerving. Hwever, the Season 4 Thomas & Friends models and sets are still used.

The episode starts out with Knapford Station, which Seventeen is rude to Duck, then Duck warns him not to go over dangerous things, that might destroy you. But Seventeen doesn't listen and puffs away to collect some freight cars (which Michael Angelis the narrator calls them trucks).

Then we see Barney (with his Season 3 voice and costume) and Sir Topham Hatt (which Michael Angelis calla him The Fat Controller) telling Percy to collect some stone from the quarry. Then Percy puffs away.

Next we see Seventeen banging the freight cars hard. The cars are angry at this and vow to pay back Seventeen. Seventeen puffs away with his cars. Then we see him puffing through the countryside, still angry.

Immediately following this, Seventeen gets sent down the wrong line. We see a shot of Seventeen rolling down the wrong line with a surprised look on his face. It is silimar to Peter Sam's S4 shocked face, except it convoys horror. The Season 3 Runaway Theme is used.

We see Seventeen roll down a steep gradient, with the cars surging against him. The shocked face from the last scene is still present. A level crossing is ahead of Seventeen, which he immediately runs into and breaks. To make matters worse, a car is on the level crossing at that point in time, which Seventeen rams into, sending it tumbling out of control.

A semi-mountainous set similar to the one from "Thomas in Trouble" (Where Thomas is confronted by the policeman) is seen with Seventeen in the far distance. The difference is that there are more rocks, ridges and cliffs, and less grass. a pair of derailed cars are present on the line in front of Seventeen. Seventeen, unable to stop, smashes into the derailed cars and flies off of the rails.

Seventeen continues to roll along the ground (a thin piece of string is visible in a few scenes) until he tumbles off a rocky ledge. He rolls down a mountain with a more unsettling face. It is similar to Peter Sam's "Eyes shut" face from Season 4, but conveys intense fear and his teeth are gritted. While this is going on, a climatic orchestral piece is heard, which is likely to be a piece of stock music.

Seventeen reaches the bottom of the mountain and crashes into the rocky ground below. A terrible, metallic crash can be heard, while Seventeen's front crumples up on contact with the ground, with bits such as whistles and handrails flying in several directions. An explosion is added for a more dramatic effect. Even worse than this is Buzz Lightyear's scream from "Toy Story 2" (when Buzz is tossed into another era by the explosion), except it is double, which I assume are Seventeen's driver and fireman, being badly injured by the crash.

As the crash dies down, the camera pans and, before Michael Angelis completes the sentence "Luckly, no one was-", we see some of Seventeen's remains, including the upturned, crumpled body shell, as an ominous strings piece (again, probably stock music) is played. Thomas and Duck see what has happened and go tell Sir Topham Hatt to get the ambulance and the breakdown train. The ambulance takes the injured driver and fireman to the hospital, while the breakdown train lifts the crumpled Seventeen, his front is gone, only his back end. He was soon scrapped. Thomas and his friends are sad about the death of Seventeen. At the end of the episode, the end credits from Season 4 played normally.