Biofilms are surface attached communities formed by bacteria and other microbes. Biofilms that form in nature typically feature different taxa, species, and multiple strains of the same species. These cells compete for nutrients and space. Due to the broad prevalence of biofilms, bacteria have evolved various competitive strategies, many of which are antagonistic. This includes a number of complex toxin delivery systems, which kill competitors but not kin. Because biofilms are densely packed, cell death and reproduction hold emergent mechanical consequences. When a cell dies and lyses, the biofilm may partially ‘cave-in;’ when a cell reproduces, it pushes other cells out of its way. This deadly competition creates a feedback loop. Death and reproduction modify biofilm structure; structural changes impact subsequent death and reproduction. In this talk, I will explore the intertwined relationship between intercellular killing and biofilm materials properties, explaining both the new physics that arises and its biological impact.