The Jade Mountain Prophecy was a prophecy given by Moonwatcher at the end of Moon Rising and at the beginning of Winter Turning, predicting the destruction of Jade Mountain unless the lost city of night could be found. This prophecy is described as the first true NightWing prophecy in generations. The plot of the second arc revolves around this prophecy.
The Jade Mountain Prophecy
Beware the darkness of dragons,
Beware the stalker of dreams,
Beware the talons of power and fire,
Beware one who is not what she seems.
Something is coming to shake the earth,
Something is coming to scorch the ground.
Jade Mountain will fall beneath thunder and ice
Unless the lost city of night can be found.
These are user interpretations of her prophecies, and while they have been reviewed and deemed accurate by parts of the community, it is important to note that they are not stated in canon.
Beware the stalker of dreams, - Scarlet, talking to Icicle via dreamvisitor nearly caused the death of the dragonets of destiny. This could also be a reference to Flame, as he came into possession of a dreamvisitor as well. This might also be referring to Darkstalker, who helped Moonwatcher out of her vision dreams.
Beware the talons of power and fire, - Vulture's organization, appropriately named "Talons of Power," and Peril when she burned the scroll, freeing Darkstalker. This could also be interpreted as Anemone when she was allied with Darkstalker, as she is an animus. Another viable option is Darkstalker himself. Another reason it could be Anemone is because of the ceremony where Turtle makes Anemone a fellow animus. The "fire" part of this probably refers to Peril, as she was the one to accidentally release Darkstalker. Yet another interpretation of the "fire" could be that it was also referring to Vulture's organization, which was setting fires.
Beware the one who is not what she seems. - Onyx, as she appeared to be a regular student, but was the granddaughter of Queen Oasis and was working with Vulture to seize the SandWing Throne; or Pyrite, who was actually Hailstorm transformed by Chameleon. It could also be Moonwatcher who talked with Darkstalker and kept her powers a secret. It could also be Cobra, who seems like she is imprisoned by Vulture but was secretly going to kill Thorn.
Something is coming to shake the earth, - Possibly Darkstalker (his size, the tremors from when he was freed, or the destruction he will cause).
Something is coming to scorch the ground. - Vulture's SandWing army, or Darkstalker and his army.
Unless the lost city of night can be found. - The lost city needed to be found so the soul reader could be collected and convince Darkstalker he was evil and provide a chance to defeat him in his hesitance. The lost city of night was also necessary to the defeat of Darkstalker due to Foeslayer turning up there and talking to Qibli (although he didn't know he was talking to Darkstalker's mother). Through their exchange, he convinced Foeslayer that her son was too far gone, and this pushed her to aid Kinkajou to put an end to Darkstalker. Also, the lost city was where Kinkajou was, so if they hadn't gone to get her, Darkstalker would not have turned into Peacemaker.