Mimic

A Mimic is a shapeshifting predator that hunts by shifting its form into a shape that blends with the environment, lying in wait for prey to touch it. Its sticky skin catches the unfortunate victim in place, allowing the mimic to either kill its prey or devour it alive. Mimics grow considerably over their life cycle: a freshly hatched mimic is no larger than a boot and feeds primarily on rats and other small creatures, whereas older mimics can take up an entire room. Rumours has it that a very old mimic might be capable of posing as a building or even a small village, but most believe this to be a mere campfire story.   Mimics tend to move and shift forms very slowly, except when they pounce. As ambush predators, they lie in wait, sometimes for months or even years, between meals. This allows them to conserve their energy almost indefinitely; live mimics have been found in sealed tombs that remained inaccessible to any suitable food source for more than a century.  

Interactions with Humanoids

Adventurers

Most famously, mimics regularly inhabit caves, ruins and various lairs - the kind of place those in the Adventuring trade would call dungeons. Most adventurers encounter mimics that are several decades old at least, large enough to take the form of a chest, cabinet, or similar, a traditional form most mimics will adopt in these environments, as these are quite likely to attract the attention of wandering prey, either in the form of an adventurer looking for loot, or just another resident of the dungeon.  

Vermin Catchers

Younger mimics tend to focus on rodents and other scavengers, making them quite useful for those brave enough to adopt one. Mimics under a decade old rarely attack humans, and are intelligent enough to recognize a human that feeds them reliably should be left alive. Young mimics are often used to protect storerooms from vermin. Mimics hunting vermin take a variety of forms, ranging from an old boot that might be a good place to hide to cheese or old meat (complete with the smell) to attract hungry vermin. All in all, mimics are considered much more effective than any cat.   Those who do decide to adopt a mimic must remember to feed the mimic as well, even if there are enough vermin to be caught for it to be decently well fed. If a caretaker stops regularly feeding their mimic, it can quickly and unpredictably decide that they have ceased to be a reliable food source and attack them. Fortunately mimics are not picky eaters - they will happily consume any kitchen scraps or leftovers left out for them. Additionally, it is wise to avoid introducing any pets or guests to the mimic - they can easily tell the difference between a person who feeds them and one who does not, but are significantly less skilled at understanding the difference between vermin to be eaten and a companion cat or dog, or an invited guest as opposed to an intruder. This becomes increasingly critical over time, as a 10 year old mimic won't even be a serious threat to a housecat, whereas a 30 year old domesticated mimic (growing faster than a wild one due to the regular food supply) can easily overpower most humans.  

Home Security

As a natural extension of their behaviour, mimics can make for excellent protectors of the home or other such facility. A domesticated mimic can realatively easily be taught to assume a specific form by first placing an object next to them for them to examine, and later leaving that object in position, and finally removing that object. On one's next visit to that room, it is likely that the mimic will be in that position mimicking that object - for example, after presenting a mimic with a small chest, then putting that chest on the bottom shelf of a bookcase, then removing the chest and leaving the shelf space empty, the mimic will recognize that's a spot it might disguise itself as a chest, and will do so. This allows someone keeping a mimic to strategically and unobtrusively place them somewhere near a particular treasure they wish to protect.