5% chance any non-player unit blows up upon death.
Boomstick is a skull in Halo Wars.
5% of all enemies killed explode, doing area damage to all nearby. This explosion can prove very useful in destroying big groups of enemies close together. This could be a big problem on the level Arcadia City, where civilians entering the escape ships are counted as dying for this skull. Meaning, when civilians enter these ships, they may end up exploding and taking the ship with them.