From SmashWiki, the Super Smash Bros. wiki
The ultimate glitch refers to a glitch in Super Smash Bros. 64 discovered by Isai. It involves picking up an invisible Bob-omb and waiting for a crate to fall on a player in the immediate area, upon which the Bob-omb would explode, causing the area where the crate fell to be engulfed in an infinite explosions created by multiple Bob-ombs. The invisible Bob-omb can be obtained by random. This can only occur if the Smash crate is a explosion crate in which it's containing more Bob-ombs.