Grain boundaries in functional oxides give rise to a large variety of emergent physical phenomena. In my talk, I will discuss novel degrees of freedom that arise in improper ferroelectic polycrystals, ranging from enhanced electronic transport at grain boundaries to unusual domain scaling behavior. The model system I will present is ErMnO3, which has attracted attention related to its multiferroicity, functional domain walls, as well as its outstanding oxygen storage capability. Scanning probe microscopy demonstrates that polycrystalline ErMnO3 develops charged grain boundaries with enhanced electronic conductance, which we attribute to distinct chemistry measured by atom probe tomography. In addition to the local transport properties, the boundaries decouple the polar order of different grains and confinement effects lead to an inversion of the classical domain scaling behavior with grain size. My research explains how grain boundaries can be used to engineer polycrystalline improper ferroelectrics, opening possibilities for next-generation capacitors and sensors.