Today we’re re-tooling the mimic. Make it more interesting because let’s face it. Most 5E standard monsters lack a certain jam, a certain je ne sais quoi. They lack MSG.

First let’s look into the lore that Forgotten Realms provides. Mimics were strange predators that assumed the form of mundane furnishings and household objects in order to attract prey.

In other words an ambush predator.

Behaviour:

Mimics had no concerns beyond surviving and acquiring food. Although some intelligent varieties of mimics were capable of basic communication, they had no culture, no moral code, and no interest in religion. More aggressive mimics could not be reasoned with in any capacity

Doug Stewart, Monstrous Manual as taken from Forgotten Realms