There are two keys on the Grave Cave level that must be obtained to complete the section. The exit is in the bottom left hand portion of the map screen, and the Talisman section is in the area of the top right section of the map. They are the slowest monsters, but if your character is cornered, they will inflict massive damage. Fight them at a distance if possible. They are slightly faster than Grim Reapers, and are very powerful when they attack.
Ghosts can combine into one another.
The brighter the ghost, the more there are. Ghosts often look around corners and are easy to hit. These monsters are fairly fast, and have a tendency to spit at your character. If one of these monsters spits at point-blank range, your character will die. Fight these monsters at a distance.