Slimes are of assorted kinds, usually marked by their overall color. They are an amorphous species, their core form being a kind of rounded dome like shape, and they can exude assorted things from their surface. Essentially all eat in the same way: they absorb the thing, enfolding itself within them. They are able to operate collectively and form a large being with a kind of hive mind that is likely about the same level as a dog.
It is said that if ever there were an intelligent slime, it could likely find a way to take over the world, and slimes eat anything. One of the most feared is the Gelatinous Cube, which seems to be an oversized version of the assorted slimes. Despite reports of the sometimes being seen above ground, they dislike the heat of the sun. One report has a massive conglomerate of Cubes acting with high levels of intelligence down in Lemuria.
There are some things that defy the mind. One of the most likely is the existence of sentient oozes, which actively move of their own will, slick and sticky, fluid and filmy. Their moist and malleable forms are excessively painful, and they love to hide and ambush prey.