Thanks you for your beautiful answer, to continue our discussions ahead, i define three different cases as per your advise.

Case 1:-Let us assume that one pendulum made up of the hollow ball and water is filled inside that. There is a hole at the bottom of the ball and water is continuously coming out from that as we start its oscillations.

Case 2:-A spring mass system is oscillating and its mass becomes double when it reaches to extreme position.

Case 3:- A spring mass system is oscillating and its mass becomes halved when it is in equilibrium condition.