Slimes can spawn when drinking from a faucet! Don't let their small size fool you, they hit hard but move very slowly. There are different colored slimes. Slimes are extra weak to ice, and resistant to fire.
Green slimes appear to have less HP, deal less damage, and spwan in the mines, and labyrinths.
Blue slimes spawn in the swamp, and in the ruins, appearing to have many more hit points, and deal more damage.
Both slimes can spawn in any faucet, even in the Minetown
"Much like the rat, you should just leave this thangs alone. They're stupid, and will just attack ya cuz yur in their way. They don't hurt much, but take an eternity to kill. And unless you kill them, they just go wanderin' about forever because they don't need food or nothin' like that. So if you can avoid them, do." ~Shopkeeper Joe
Slimes don't drop anything.