The Ghost is the ultimate danger in Spelunky. With 9999 health it is pretty much impossible to beat under most circumstances, it can not be deterred, and one touch is guaranteed death.
Fortunately, however, it is possible to make it through the entire game without ever seeing it.
Unlike many enemies in the game, the Ghost is more of a disincentive than an obstacle. It exists to prevent loitering by greedy treasure hunters, and 'turtling' by overly trepidatious delvers.
Instead of allowing the player all the time they need to meticulously sweep every level of treasure and to take as long as they like to creep around difficult traps and enemies, the Ghost introduces a dynamic of play where risks must be taken and good judgements must be made quickly.
By putting pressure on players to improve, the Ghost ensures that the only way to be successful is to hone your skills and play well.
The Ghost is invulnerable to most damage and will pursue the Spelunker relentlessly. The only real 'strategy' available is to simply run away to the safety of the level exit.
It is possible to temporarily stun the Ghost by taking a picture of it with the Camera, which causes it to pose humorously. This does little more than delay its pursuit, but the brief second it spends distracted might just be all the time you need to slip past it and get out of an otherwise hopeless predicament.
'Killing' the Ghost
Due to a programming oversight, it is possible - albeit extremely difficult and time consuming - to kill the Ghost. The Ghost has 9999 hit points, and only takes damage upon entering lava (99 damage at a time) or by a UFO shot passing through it (1 damage). It would take 101 hits for the Ghost to die if entering lava . As the Ghost was never expected to die, there is no death animation when its health reaches zero - the Ghost simply disappears.
It is also possible to kill The Ghost by making it stay for a small amount of time in The Abyss, this will make the Ghost fully disappear during the current level.
There are three circumstances where the Ghost is summoned:
After 2 minutes and 30 seconds spent on a level, you're given a warning: "A terrible chill runs up your spine!".
This signifies the arrival of the Ghost, who appears from beyond the edge of the level closest to the Spelunker.
Its ominous appearance causes the atmosphere of the level to change as a spectral fog sets in and the background music becomes distorted.
At this point you should prepare to leave the level as soon as possible, but this deadline is negotiable if you are able to evade the Ghost and avoid being cornered.
The Ghost does not spawn in this manner on levels 4-4, 5-4, and in the Worm, as these are special levels that are expected to take a long time to complete.
Disturbing the Crystal Skull
If the Ghost has already arrived on the level, picking up the Crystal Skull will actually cause a second Ghost to appear from a side of the level.
Finally, destroying three or more of Kali's Altars in a single game will enrage the vengeful goddess to the point of immediately spawning the Ghost. You will have to deal with the Ghost in addition to being shackled with the Ball and Chain.
Though this won't affect the invisible level timer, no further Ghosts will spawn if it hits 2 minutes and 30 seconds.
The Ghost will then spawn in every subsequent level immediately after entering, except in boss levels where it doesn't spawn until the cutscene finishes.
Using this method, destroying the third altar in Hell will make it possible to convert Yama's throne of rubies into diamonds. This was done by Gaming-In-The-Margin.
For the daring and agile, the Ghost can be used to generate extremely valuable diamonds.
When the Ghost passes over large rubies, sapphires or emeralds lying on the ground, they will be transmuted into diamonds worth several times the value of the ordinary jewels. Gems still embedded in rock will not be affected.
Unearthing jewels and leading the Ghost over them deliberately is known as Ghostrunning, and can result in astronomically high scores if done well.
The general strategy for Ghostrunning is proper planning, the Spelunker should make sure of always having a way out and never getting cornered.
It's also worth noting that the Ghost hitboxes for Ghosting gems and getting the player killed are different, the player can be a bit inside the Ghost without dying, but gems can be Ghosted even if they are just barely touched by the Ghost, because of this, the player has the possibility to jump over the Ghost even without the need of Spring Shoes or Shotgun jumping as long as the Spelunker makes the jump at the right time when the Ghost is at the bottom of its normal movement. If playing multiplayer, dead Spelunkers can blow the ghost away momentarily delaying it. However if the ghost is blown too many times by a dead Spelunker in multiplayer mode, it will go at the speed of a running Spelunker for a few moments, so caution must still be exercised in this situation.
- The Ghost may be a reference to the ghost from Ghost Face, but it functions more like Baron von Blubba of the Bubble Bobble series, who operates as an invincible (but avoidable) enforcer of the stage time limit. Baron von Blubba is accompanied by an ominous theme tune, much as the Ghost in Spelunky warps the background music when it appears.
- The Ghost may be pushed around by UFO explosions, which may cause it to appear to 'dash' towards you.
- Under certain circumstances, up to three Ghosts can be spawned at once. For this to be possible, you will need to enter a Jungle level with both "Restless Dead" and "Flooded Cavern" Level Feelings in effect.
The first Ghost will appear once the time limit elapses (or sooner, if Kali has been sufficiently angered), the second will spawn by picking up the Crystal Skull, and the third will appear by killing Old Bitey, as a result of him dropping an additional Crystal Skull during Restless Dead levels.