Snail

Groups of snails naturally spawn in swamps. They can't handle saltwater, so the swamp is perfect!

Snails are an adorable, portable slime farm that spawn in swamps. When fed beetroot, they have a 1% chance per second to spawn mucus, lasting for 20 minutes. When fed heartbeets, this chance increases to 5%.

You can also breed two snails together using beetroot soup. Then, wait for the pregnant snail to lay its eggs into a clay block beneath it. Then after about 30 minutes, more snails hatch from the block along with lots of clay and mucus.

There are six total variants of snail: Yellow, brown, black, cyan, spiral, and the final secret variant.

To find that variant, you'll have to take a snail nest using silk touch and go do some soul-searching in the nether...