I think that was on a timer? What I want to know is what happens if you dig a spiked pit under all the spawn locations. Also those skulls are absurdly exploitable.
Edit: Also train-chan is only in the starting town.
@Speak_Evil A train is when a person runs through groups of enemies without killing them. The monsters target the person and give chase, forming a train. If the monsters are killed then the train can't form.