In the entity .FPE, add
ischaracter = 1
This will allow you to assign enemy AI to it.
Beyond that, you will need to do some custom scripting to get the behavior how you want it.
This guide will help you get started with scripting.
Once you are familiar with the basics it will be easier to find help here on the scripts board.
I also recommend opening and having a look at one of the included enemy character .FPEs to see what kind of additional details you will need to be aware of.
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