Well, the monsters in the movie are essential for building the world of Solo: A Star Wars Story. Take the Mudtroopers for example. They are part of the Empire's military presence, and their presence makes Han's smuggling operations more difficult. This, in turn, drives the plot as Han has to find ways to outwit them. Also, the other strange creatures like the space worms add an element of the unknown and danger to the various planets Han visits, which makes his adventures more exciting and gives a reason for his character to develop survival skills and strategies.
The monsters play a significant role in the overall plot of Solo: A Star Wars Story. The space worms on Mimban, for example, are not just there for show. Their existence forces Han and his team to be more careful and strategic in their movements. This cautious approach leads to different decisions being made, which then affects the flow of the story. The Kessel Run monsters also contribute in a similar way. They are a threat that Han has to overcome, and this process of facing and defeating or evading them helps to shape Han's journey from a young and inexperienced smuggler to a more capable and confident one. Without these monster - related challenges, the plot would lack the excitement and the character - building elements that are so important in a Star Wars story.
The monsters create obstacles. For instance, the ones on the Kessel Run force Han and his crew to use their piloting and combat skills to survive. This helps in showing Han's growth as a character.