This variety of mimic has learned to imitate not only the appearance of armor, but its durability and protective hardness.  Armor mimics often sneak their way into castles or armories where suits of armor are sure to be displayed or stored. 

Armor mimics allow themselves to be dismantled and donned, with each piece of armor connected to the breastplate through thin, nearly invisible strings of amorphous flesh.  Once an armor mimic has been donned, the creature wearing it is all but doomed, practically already in the mimic's stomach.

However, many armor mimics are intelligent enough to realize that feeding in this manner is a sure way to be discovered, hunted down, and killed.  Instead, they prefer to offer their formidable armored hides in service to adventurers or guards in exchange for regular payments of food.

Variant: Mimic Armor

Some armor mimics are willing to serve as armor for other creatures in exchange for regular payments of food. A mimic acting as a suit of armor gains the following trait:

Mimic Armor.  The mimic can be worn as a suit of armor, and functions as whatever armor it polymorphs into.  Regardless of what type of armor it is polymorphed into, the mimic does not have a Strength score requirement and does not incur disadvantage on Stealth checks.  A creature wearing the mimic has total cover against effects outside the mimic.  Attacks made against the wearer are made against the mimic instead.  While acting as armor for another creature the mimic takes no actions of its own, and is no longer immune to the prone condition.  Additionally, the mimic shares its Adhesive and Grappler traits with its wearer.

The mimic's wearer can don or doff the mimic as an action. The wearer can also command the mimic to cast a spell from the mimic's Innate Spellcasting trait, requiring the spell’s normal casting time and using the mimic's spellcasting DC.

The mimic is immune to game effects that would damage or destroy armor with acid such as a black pudding's Pseudopod attack.  Non-acid game effects that would damage or destroy armor deal 1d10 damage to the mimic instead of lower its AC.  If an attack or game effect would reduce the mimic to 0 hit points while it is being worn and its wearer has at least 1 hit point, the mimic drops to 1 hit point instead.  While the mimic has 10 hit points or less, it loses its Damage Transfer trait, its wearer takes all damage dealt to the mimic in the mimic's stead, and the wearer loses all benefits provided by the mimic.  The mimic is considered a destroyed suit of armor until its hit points rise above 10.