Darkstalker's Teeth is a mountain range mentioned in Darkness of Dragons. Winter mentioned that he couldn't go over them, because no IceWing had flown over them and survived. This was due to Darkstalker's forcefield that he created over this area. However, Winter got over fine, because he was wearing a protective earring.
After a short debate with Clearsight and Vigilance over how to keep the IceWings out of their kingdom, in which Darkstalker suggests multiple times they wipe out the entire tribe, Darkstalker enchants a forcefield to kill any IceWing flying through.
Qibli, Winter, and Anemone meet near Darkstalker's Teeth. They discuss several things until Winter says he can't go over the mountains without dying mysteriously. Qibli tries to convince him that everything will be fine, pointing out that Winter is wearing an enchanted protective earring. Winter finally agrees and survives.