The Monolith is a bonus grenade unlocked upon completing Metal Slug 3D once.
Effect
The monolith, when thrown, shoots a beam into space, and then brings down a big tablet crushing any tanks or people under it. The only disadvantage is that there's a small second delay for it to take effect.
References
- This grenade is based on the Metal Slug 3 boss, the Monoeye UFO, which uses a nearly identical attack.
- It is possibly a reference to the film 2001: A Space Odyssey.