Nurgling
Nurglings are the lesser daemons of Nurgle who are with affection referred to as 'Nurgle's little boils' by his worshipers and as 'vile pusbags' and 'arrrrghh what the hell is that thing?!' by everyone else. Despite this, their models are alarmingly cute. They are born from the pustules and tumors that grow inside a Great Unclean One, although any stalwart follower of Nurgle is able to give birth to one of these through his own skin.
A Nurgling looks like a miniature version of Nurgle himself: a tiddly bloated man-shaped critter, crawling with disease and difficult to look at (like all daemons). They rarely reach over a foot in height and as much in width. They are playful creatures, often demanding constant attention and frequently rough and tumble with each other. The Great Unclean Ones laugh at the antics of the Nurglings and pat them with affection and shower them with scraps of meat. There are sometimes eaten as snacks though, not that this matters much, as they simply crawl out again of some an open wound or another. Other worshipers of Nurgle are not so forgiving of the Nurglings; the Plaguebearers see them as irritating nuisance that gets in the way and makes jokes about the serious matters of life and death (although they do secretly have a soft spot for them). Granted it's only soft because it's rotten, but it's soft all the same... I forgot where I was going with this...
Individually, a Nurgling isn't physically powerful and not a threat in itself; it is the diseases that inhabit them that are the true threat. To let them touch you is to invite lethal pathogens inside your biosphere. Their combat strength is in numbers; Nurglings will often drown much tougher enemies in endless swarms that move like rivers underfoot of advancing Nurglite armies.
Just like most other pets in W40k and Warhammer Fantasy, Nurglings can and will willingly perform tricks. It is highly recommended to bring a Nurgling to a karaoke night, as it's connection to the Warp and daemonic power could be used as magnifier for your voice to turn into a magnificent wail. After the success that karaoke night will obviously be, make sure that your lovely voice will not attract any lonely daemonettes. The most lethal weapon against a Nurgling is a broom, the best tactic against a swarm is a good ol' fashion flamethrower.