Transylvania Traintracks is another term for laced coffee, or coffee with another substance in it. Coffee that has trace amounts of LSD, Cocaine, or any other drug inside of it would be considered Transylvania Traintracks. The reason it is called Transylvania Traintracks is that the Romanian scientist (Romania is modern-day Transylvania) was killed with laced coffee. The "Traintracks" part is there to remind you that it hits you like a steel train.
I just ran a train on those Transylvania Traintracks and I feel like shit now.