This is the armor of what was once a Deathknight, but it still contains the whisperings of sentience. Once a creature dons this cursed armor, they can't doff it unless they are targeted by the remove curse spell or similar magic. While wearing the armor, they have disadvantage on attack rolls against Demon Lords and on saving throws against their spells and special abilities. (1/Day) The armor issues a command and demands the creature to fulfill the Oaths of the Faithful of the Kahlab, they must contest the armor's Charisma (Intimidation) check against their Wisdom (Insight) check or follow the command, ignoring any moral compunctions they would normally have. If the armor loses the contest, it will attempt to slowly crush the creature into submission, dealing 1d4 bludgeoning damage each round until the creature dies or acknowledges the armor was right.
Note on Cursed Items: (DMG 138)
Cursed Items: Most methods of identifying items, including the Identify spell, fail to reveal such a curse, although lore might hint at it. A curse should be a surprise to the items user when the curse's effects are revealed.
If it requires attunement, you are not only cursed as long as that attunement exists, but you are prevented from ending the attunement on your own voluntarily.
Remove Curse, or Greater Restoration will end attunement to a cursed item long enough for it to be removed, and the character freed from that curse, but will NOT end the curse on the item.
The only methods to remove a curse on an item typically is the use of a Wish, destroying the item entirely, or in the case of a deliberate curse being cast during creation, the caster must release it.