After purchasing the Homecomingcampaign, beating its mission Short Fuse unlocks a playset of Casualties of the Cause.
Premium versions of Casualties of the Cause also unlock if the premium campaign is purchased. Without it, the premium cards can be crafted for 1600 Shiftstone each, after being unlocked in the mission.
Because most sites have 4 or less durability, Casualties of the Cause can function as a good anti-site card.
Casualties of the Cause's 1-damage downside can be used to trigger the RenownRenown: Does something the first time you play a spell or weapon directly on it. abilities of your units, letting you get some additional value.