Grad mal im Wiki geschaut:
[Treasure Keys] can drop from Izaro, Argus, Treasure Chests or Curious Lockboxes.
Curious Lockboxes sind immer in Silver Caches (man benötigt also einen Silver Key um zum Cache zu kommen).
Izaro kann mehrere Treasure Keys droppen, abhängig davon, wie man die Kämpfe gegen ihn führt:
The first two encounters with Izaro add new mechanics to the fight that carry on to the next encounter(s). The mechanics change daily alongside the layout of The Labyrinth. Izaro will be encountered in a room containing three small holes in the ground that will introduce the additional mechanics for that particular fight. A Forbidden Reliquary room contains a trinket which makes the mechanics easier to deal with.
Any mechanics that have not been dealt with will carry over for the subsequent fights. However, leaving the mechanics untouched (Ex. don’t destroy any portals, have all three idols activate, don’t activate any charge disruptors, etc.) will result in Izaro dropping an additional Treasure Key on death.