Silkie
A silkie (sometimes known as a brownie) is a household fairy which usually comes out at night to tend to chores left unfinished around the house. They are incredibly shy, thus why they operate at night, and use magic to hide little doors in the walls of the house they're in which lead to their own tiny rooms.
The treatment of a silkie, as indeed with any living thing, directly determines its attitudes and behaviors. A happy silkie will clean the home, will do chores and odd jobs willingly and without any mischief (well, maybe just a little.)
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An unhappy silkie, it is safe to say, will make the homeowner thoroughly miserable. No tidying will be done unless it is to cause confusion and upset. There are even some cases where a silkie is so angry it turned into a boggart (a malevolent spirit).
Silkies have enormous black eyes, sallow skin and silvery hair. They seem not to have any nose or mouth, however, when given milk as an offering, it has been known to drink it. How exactly it does that is anyone's guess.
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Silkies can disguise themselves to look like children and frequently do so when confronted by humans. Though it must be noted that on very rare occasions, seemingly when the mood takes them, they do not disguise themselves and take great delight in terrifying the residents of the house.