Train Derailment - known as "Ecliptic Express Incident" (黄道特急事件,Ōdōtokkyū jiken?) in Japan - is the first section of Resident Evil: The Umbrella Chronicles. It is based around the events of Resident Evil 0, set during July 23-4, 1998. The titular levels are unlocked first, with the other two being unlocked later. The following levels are listed in chronological order:
Billy is seen using a Colt Anaconda, which is not obtainable in Zero.
Billy's introduction has him saving Rebecca from one of the zombies, when in Zero, Rebecca's first encounter with the zombies and her encounter with Billy were in two different places.
In Zero, Rebecca and Billy attempt to stop the train. In UC, the crash is a complete surprise.
The Giant Bat is fought on the rooftops of the Church. In Zero it is fought inside the Church.
Billy and Rebecca never actually encounter Dr. James Marcus at all until arriving at the B9 microwave furnace room in UC. In Zero, they witnessed his younger self outside the train, and encounter his old self multiple times starting with on the train as a Mimicry Marcus, although they only learn about the extent of his connection to the deceased Umbrella researcher upon encountering him in the aforementioned room.
In addition, Marcus himself does not use his younger appearance at all during their encounter in UC, instead opting for a sickly-green facsimile of how he appeared before he died.
In UC, Dr. Marcus is shown willingly transforming into the Queen Leech shortly after making his speech to Rebecca and Billy. In Zero, Dr. Marcus, if anything, had forcibly reverted to his Queen Leech form.
Certain layouts for the levels were different compared to the original game. This was most noticeable with Train Derailment 3.