The Grunt is part of the I.D.P.D.. Unlike other I.D.P.D. units, Grunts will spawn in pairs. The amount of Grunts that spawn from a single portal increases on loops. Each loop adds one more Grunt. Grunts are also summoned by Lil' Hunter during his pre-loop boss fight.
Grunts have two different attacks:
Their main attack is to shoot blue, fast-moving bullets. They shoot a single bullet or in bursts of up to 6 bullets at a time. Unlike every other ranged enemy, all I.D.P.D. troops (including the Grunt) can shoot your character from point blank.
The second attack is a blue I.D.P.D. grenade that will glow (in the same way their portals do before spawning) before bursting into a large blue explosion that can deal 8-16 damage. Unlike regular explosive weapons, these grenades won't damage I.D.P.D. units.
They also have a movement ability that is similar to Fish's dodge roll.