How do animal embryos control the large-scale tissue deformations and mechanical properties required for their form and function? And can we design materials that do the same? Recent work by our group and others suggest that one successful strategy is to poise the system close to a fluid-solid transition. Much like a glass-blower shaping a glass ornament, targeted fluidization of the material facilitates large deformations, while targeted solidification freezes in desired shapes. In this colloquium, I will discuss recent theoretical work to describe the entire design space of possible floppy-rigid transitions in a class of materials that includes fiber networks, confluent biological tissues, and mechanical metamaterials. In related work, we investigate models for confluent tissues with physical-learning-inspired feedback rules that can drive specific flow and deformation, e.g. convergent extension, and compare to experimental data for germband extension in fruit flies. I will also discuss emergent mechanical properties and design principles in a different class of materials -- highly sparse cellular networks -- such as those found in mesenchymal biological tissues.