In Massivly Multiplayer Online Role-Playing Games (MMORPGs) the term train discribes a large group of monsters chasing someone to the edge of some zone, In older games they would usually result in a long line of people getting their digital behinds thoroughly kicked. Sometimes this was intentional but most of the time it was just cause of some fellow biting off more than he could chew.
...And other times it was part of a plan to use a poor sap as a decoy in order to get all those monsters out of the way, this was one of those times.