Phoenix Logs/Banished Units/Grunts (Brute)
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Expendable minions [and they know it].
Though derided as cannon fodder, there is no mistaking the military value of having an almost endless supply of cheap infantry armed with plasma pistols to hurl at a foe. Each Grunt squad is led by a Brute armed with a spike rifle who can be upgraded to plant a cloaked proximity~fused shrapnel mine on the battlefield. The Grunts can be upgraded to add a pack brother and lackeys.
Grunts may not be strong, brave, intelligent, hygienic, or particularly fearsome warriors, but those forced to serve the Banished have a healthy enough fear of their Brute leaders to stay on-task and motivated. Even if their fellows are used as target practice by bored Brutes or disintegrated by Forerunner sentinels, the survivors can at least look forward to a full food nipple and a brief nap in the methane atmosphere they call home.