For FPS mode, the mouse should work.
I downloaded Open Dungeons version 07.1, would run it in Windows 10, there is no mouse available to move around with, only arrow keys.
Mouse movement in DK was very well scripted, you could also adjust the sensitivity of the mouse.
In DK, walking in FPS means using both the mouse and the arrow buttons. Can be used for reconnaissance, you can use it for imps to run over lava until they die there after 4 or 5 tiles. Some secret levels and one Deeper Dungeon level can not be completed without the FPS mode, several custom maps use FPS mode also.
FPS mode takes over a creature completely, and uses lenses where very creature has a different filter to the camera. I found a nice examples of lenses to maybe use over here, made in Ogre3D Compositor:
https://www.youtube.com/watch?v=BQyXeSgle7cExcept for the camera from the instance of the creature, the tab on the creature's properties was visible next to the FPS view.
I did not see any portrait of any creature yet in Open Dungeons, at best they could be made by using renders from Blender.
In DK, every creature had a name, and their properties where a databank of facts.
Except maybe for the blood type, this will have been added to fill up a slot, or to make the game more impressive, the creatures more real.
Another problem for an FPS mode, is the ceiling.
The ceilings in DK, can only be seen in FPS mode.
Ceilings where scripted to become higher, once the space between walls was wider.
Ceiling has to be implemented also, to create the FPS mode.