Although as far as rake, speed, priority and facilities and concerned, 10112 and 10104 are twin-trains. Just that 10104 gives you a day-time journey on the Konkan coast with interesting on-boards panty car services while in 10112, you'd mostly be sleeping in major part of the journey.
Mandovi (10104) is for those who want to enjoy the journey while Konkan Kanya (10112) is for the busy people who wish to save a day by travelling overnight.