Short answers, pulled from the story.
Nymphs in ancient Greek mythology were credited with healing powers through their association with springs, the ability to divine the future, and the power of shapeshifting. Encountering one alone could inflict dumbness, madness, besotted infatuation, or stroke on a mortal.
Greek mythology recognizes many types of nymphs grouped by habitat. The Naiads were nymphs of fresh water, the Nereids were fifty daughters of Nereus and Doris who inhabited the Mediterranean Sea, the Oreads were nymphs of mountains and grottoes, the Dryads belonged to oak trees, and the Meliae were nymphs of the manna-ash tree.
No. Despite their divine nature, nymphs were not immortal. This set them apart from the Olympian gods and placed them in a distinct category among supernatural beings in Greek mythology.
Ancient belief in nymphs survived in many parts of Greece into the early years of the twentieth century, where they were known as "nereids." When parents believed a child had been harmed by these beings, they would pray to Saint Artemius, a choice likely reflecting a corruption of the name of the goddess Artemis.
The sleeping nymph motif entered European art during the Renaissance, traced to an Italian report of a Roman sculpture at a fountain above the River Danube. Both the report and the accompanying poem are now generally concluded to be a fifteenth-century forgery, yet the motif remained influential for several centuries, with copies appearing in neoclassical gardens such as the grotto at Stourhead.
Since the Middle Ages, nymphs have been popularly associated or confused with fairies, appearing alongside elves and elusive beings in medieval romances and Renaissance literature. Both figures share characteristics: they are female, tied to wild or liminal places, capable of harming humans, and associated with areas at the edges of human settlement.