Explosions have twice the damage radius. Light fuse, run away.
Location (Halo: Combat Evolved Anniversary)Edit
This skull is located on the mission "Halo," right after you first get the warthog. Instead of going downhill to enter the Forerunner cave, go right until you are above the cave. The Skull will be on one of the cliff ledges.
Boom Skull location video here
When Boom is activated, all explosions have double the explosion radius. As well as grenades and explosive weapons, this also affects Grunt Funeral explosions, Sentinel death explosions, and scripted ambient explosions such as those on The Pillar of Autumn and The Maw.