A uncommon ymir 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 Uncommon Ymir Chest in Evony TKR says:
Open the package to gain all the items in it.
Uncommon Ymir Chest is known to drop from a number of bosses or monsters upon killing, including Ymir.
Note: This list may be incomplete.
Uncommon Ymir Chest opens up to all of the following items: