Animating within video games - Robot designs

Now we have a finished main character that the player will be controlling, the next stage is to come up with the enemies. The idea is to come up with a futuristic theme using robots that guard the corridors of the laboratory. Here I have a few sketches that I have come up with.

At the moment we only have rough designs. We are aiming to have 3 separate robots - A small robot which can be killed with one hit and has less detail on it. The medium robot which has a bit more detail on it and is slightly bigger than the small one. Then there is the large robot which has quite a lot of detail on. The robots get more difficult to defeat, the bigger they are the harder to defeat.

I have come up with a video to represent the idea that we are going for. The video shows how the robots are different sizes and have different features. They also have very different weapons that attack the player. The video also shows how we want  the player to take over the robot once they have defeated it. So the player goes up a level when they defeat a robot by becoming that robot itself.