If you have to travel unreserved in this train, the farthest station you can board from and get a comfortable seat is Surathkal. After Udupi, there is no chance of getting a seat in the General Compartments.This is only during the lean season and on weekdays. During the peak season, the train gets jampacked at Mangalore Junction itself. Avoid travelling unreserved at all costs. The journey will be horrible. Try to somehow get at least a RAC ticket in any of the reserved classes.