If necessary, you could always make a 'parallel' map, so that the tracks for the train would be isolated from the outside. When the player turned into the train, the maps switch, so suddenly you are on tracks and can move only on the tracks. If you make the map smaller, also, it appears that you are moving faster. You could also simply set this up for a development thing, and do it once, being filmed by Snapz, and simply put in the movie, and then it would just appear to have the train move. Of course, you could also split this movie in half, and at halfway give the player his sprite back and put in a section on the train interacting with characters, followed by giving the train thing again, then putting the player on the map as his normal self again. That would be like FFVIII.
Can you tell that I came up with the train theory? This would work with boats too.
Hope this helps,
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Subcommander g'Var "8 Lightnings" Krai'un
Second in command of the Escort Starbeam.
“Imagine if you will, you’re standing on a grade of finely processed salt in a salt factory. Now, there is a very large rusty blade flying towards you at a very high speed. Imagine now, the feeling you will have as you fall into that salt after you are run through with that blade.” -Marathon Infinity, Terminal 0, Page 2, You Think You’re Big Time, You’re Gonna Die Big Time, Vidmaster’s Challenge Edition.