Multi-Hit Vanish Blox do exactly what they say, the vanish after multiple hits.
They usually appear as regular stone, but in some cases may be different. In Boom Blox Bash Party they appear similar to the moon's surface while in the outer space stages.
They will be destroyed after multiple hits of a toy, character attacks, or explosions. In some multiplayer levels in the original Boom Blox they are colored to match a certain player. In the sequal, this role is taken by Hull Blox