Recently, organic crystals with mechanical flexibility have been emerging as a hot research topic due to their great potentials in flexible optoelectronics. However, organic crystals exhibiting elastic bending or plastic bending are relatively rare. In this study, we proposed a strategy to improve the probability of crystal flexibility as well as to regulate the mechanical properties by controlling polymorphism. Three different emissive organic polymorphs Cry-G, Cry-Y, and Cry-O with elastic, plastic, and brittle natures, respectively, were obtained by fine-tuning crystallization conditions of a diaryl β-diketone compound. Cry-G was found to transduce light and amplify the self-waveguided emission efficiently along the crystal body in the elastically bent state, demonstrating its multifunctional applications in flexible optical devices. This study is of great scientific significance not only to engineer mechanical compliance of organic crystals but also to highlight the utility of "crystal flexibility".