Meyems are dreamons who try to blend into an environment by mimicking objects in the vicinity. Theyre slight pranksters but not malicious. In fact with lots of contact and kindness they can become friendly and helpful. 

Sleyems are very low tier dreamons that pretty much only think about eating. These critters are more or less scavengers and not good with confrontation so they tend to stay in places like vents and drains until everyone is gone where they will then come out looking for something to snack on. Theyre not malicious but they do spook easily. Their slime has a thicker film on the outside so that folks can touch and pick them up but be careful not to press too hard. The goopier slime under the film is highly acidic. 

They can also fuse to form bigger sleyems like this:

Next are some more sentient dreamons, Handsels and Greyettels.

These two dreamon types always work in a pair. Handsels do well with handywork but tend to be clumsy so Greyettels tag along to monitor their work to make sure it is done properly. You’ll see pairs of them mainly helping the Red Dept. They may accompany other employees to help them make a task go faster if its a big job. They are all referred to as handsels and greyettels, its rare that they have names other than those.

Next to answer your question about Fairy, they are a lesser Dreamon. They are known as the Dreamon of Sweet Dreams but they dont fall into the category of Hueminns which includes oranhamme and his kin. Fairy is the only dreamon of their kind and there are other dreamons that are also unique like Baruti.

(Not to scale)

These kinds of dreamons basically have more specific purposes and special abilities to aid them in carrying out their designated task. For example. Baruti is a chief dreamon under Violson and has great powers of clairvoyance and more. Fairy as the dreamon of sweet dreams has powers that help folks have well…sweet dreams.