Grenadiers were SwarmDrones who specialized in close quarters combat. Identified by the chalky white war paint adorning their chest and shoulder, they typically used Gnasher Shotguns and Bolo Grenades to flush enemies out of cover.
Grenadiers are essentially the same as standard Drones, possessing the same amount of health, but their weapons make them a different threat. They'll stand up out of cover once they start twirling their grenade, so take them out before they can throw it.
The Grenadier is a playable multiplayer character for the Swarm in Gears of War 4, and has three unlockable character skins, excluding its Default skin: Color Blast, Onyx Gold, and Spectre. Its Onyx Gold skin is only available in the Onyx Gold Swarm Pack.
The Gears of War official website provided a cosplay guide for the Swarm Grenadier, located here.