The blue beam refers to the in-game phenomenon where players see a blue beam hitting them or close to them before dying. Players have seen enemy units also being killed in this manner.

Many thought these blue beams was evidence of cloaked Illuminate Hunters due to similarities with the Hunter’s sniper shot from Helldivers 1.

Later, it was discovered that they were caused by spike plants, an environmental hazard. Shrapnel from the plant would cause insane damage. It is similar to Eruptor shrapnel damage behavior before it was patched out.