A legendary witch chest is an item in Evony TKR (The King's Return). It can be found after killing certain monsters or bosses, with some of them listed below.
The description of Legendary Witch Chest in Evony TKR says:
Open the package to gain all the items in it.
Legendary Witch Chest is known to drop from a number of bosses or monsters upon killing, including Witch.
Note: This list may be incomplete.
Legendary Witch Chest opens up to all of the following items: