Complex sentence: One of Mountainshadow's agents or alter-egos is called "Dark Tooth" (the English translation of the German "Dunkelzahn"), implying that Dunkelzahn and Mountainshadow are the same dragon at different points in history.
Split into simpler sentences: One of Mountainshadow's agents or alteregos is called "Dark Tooth" (the English translation of the German "Dunkelzahn"). It is possible that Dunkelzahn and Mountainshadow are the same dragon at different points in history.