Anskum-pattern plasma grenade
From Halopedia, the Halo wiki
Summary
This Covenant weapon is similar to the human hand grenade in that it is a thrown anti-infantry and anti-vehicle weapon. It sticks to targets by coating itself in a thin layer of plasma which, when in contact with a target, fuses to the target and is impossible to release. It has some kind of internal mechanism that allows it to distinguish between targets and background. For example, it will stick to a soldier or vehicle, but not a tree or wall. It has a three-second fuse that is activated after it sticks to a target or otherwise comes to a rest.
If one plasma grenade sticks to another plasma grenade, their explosive cores fuse and generate a larger explosion.
It should be noted that prolonged exposure to the radiation emited by plasma grenades can cause a deviation in the neural electric pathways of the user--a disorder called Boren's Syndrome, which in one case renders them immune to infection by the Flood.
Another thing to note is in the most recent update in Halo 2, the Plasma Grenade has an instant kill effect if it goes off at the base of the target's feet (Does not have to be stuck).
If you stick a charging Hunter with plasma grenade the hunter will instantly turn around, exposing its back, when the grenade explodes.
