User blog:Drake Alcander/Grimm Growth

Theory: In the World of Remnant episode on Grimm, we learn that when Grimm are slain, nothing is left behind. We also learn that they do not seem top require to eat to survive, only killing/ feasting  on wildlife when territorial issues arrive. Finally, we have it explained to us that the longer a Grimm survives, the larger and tougher it becomes.

My theory is that as a Grimm grows older, they absorb more particles of dead Grimm in the air, giving them more mass.