Not enough light and too much water, most likely. The stretched part at the base of the leaves (also a different color green) would seem to suggest the plant has not been getting enough sun. Is that a north facing window? Have you moved the plant lately? The dead leaves are nothing to be concerned about. The red part at the base of some of the new leaves would suggest that the stem may be rotting. Are they soft? Do those leaves release from the stem if you tug gently? If you tug on the offset in photo #3, does it release from the soil?