Game developer RDStoat demonstrated a nice trick you can use to "fake" 3D enemies. For their third-person 2.5D action game, they needed to figure out how to dodge attacks that don't actually move towards you and how to rotate around an enemy that is actually a flat sprite.
The solution was to make the enemies seem 3D even though they aren't. The 2D pieces move with the character's view and look surprisingly three-dimensional.