Spelunky is a very difficult game. But of course some people aren't satisfied with just plain difficult. Bananasaurus_Rex has already done the near-impossible solo eggplant run, so he had to invent a new challenge for himself.
If you aren't familiar with Spelunky, it's a platformer with randomly-generated levels. If you spend too long on a particular level, a ghost floats in and starts following you. One touch from the ghost kills you instantly. B_Rex apparently got curious if the ghost itself could be killed, and asked someone to use Cheat Engine to find the answer.
The result is this video from HecticXXX9001 who made himself invulnerable to test out the theory. He does a good job explaining why they're doing this and how it works:
Once that was figured out, Bananasaurus_Rex got to work and did it without cheats, resulting in the video above. If you want to see the whole run up to the ghost, you can check it out here.