Dummy Entities are Superfluous.
One of the main design issues (it was a nice idea in the multiplatform case) is that we are not attaching the information related to the GUI to the Entity class. This is problematic because the GUI needs this information when working with Entities, while using only the GameState.
More explicitly, in order to create a gamestate which is usable by the GUI we need to perform casting in a most horrible way (and this is not the only place where we do it). Another potential solution will be to create something similar to a GUI GameState, but I believe that as we will be dealing with many types of Entities this adds unnecessary complexity.
Proposal: Combine the DummyEntity class with the Entity one.