is there a way to make the boomers trigger each other, or even nearby trap chests, without making them do full damage to everything else? Like giving them a bonus to damage against boomers/chests or making boomers/chests more vulnerable to the damage? Maybe give them a 2nd damage type that only affects boomers/chests?
I don't know if there are multiple damage types in the game already or not, but it seems like it'd be a good thing to incorporate. Physical, Fire, Explosive, Holy, Unholy, etc... and then you could make each unit more or less vulnerable to the different types to really differentiate the units in what they're strong or weak against.