When Vitruvius visits Emmett as a ghost as he is strapped to the battery, he is floating because he is attached to a string.
image from here.
Now, I assume this is because Finn is playing with him. But why is it being explicitly shown? Everything in the movie is being played out by Finn in the basement with his Father's Lego sets. So, for e.g., Superman is not really flying but being moved around by Finn.
So why is the Ghost of Vitruvius not floating on its own? Why does it need to be made explicit that Finn is the one who is moving him around using a string?