At the moment I am making a CS for the 'bad guy' type role. An insane-ish dark spirit of some kind - that has the ability to possess weak willed/minded creatures/people.

Depending on what you had in mind he/it could have a bit of a running rivalry with Ada and hence attempts to play with/interfere with the main character? (Should have the CS up soon for your judgment and suggestions). 

Anyway, just some thoughts. If need be I can always make a CS for any other character at your request :)