Even with the character in Public Domain, I doubt Disney would be particularly happy with anyone using it.
They can send cease and desist letter left and right, claiming that "the use of the mouse is fine, but the elements X, Y and Z were introduced in a later work of ours that's still protected", even if it's a plain lie.
Trying to take Disney to court is suicide.
The have enough money to hire half the lawyers in the world and make them come up with a lawsuit even if there's no basis for one. They can stretch the lawsuit process to last years, and yet the fees would be but a fraction of a fraction of a percent in their yearly spending. Almost any defendant, meanwhile, would be financially ruined by it, even if they end up winning.