I started the mummy quest after 200 hours, I had a leader position, I have 100% in every single spell.

Previous PBFs for other mummies have indicated that this should have been >50 and likely around the 70 mark.

Are you able to inform me why it was so low?

Is there a -base factor for not having a role?
EDIT: No it doesn't appear to be a factor. This necro had no role when he became. Only added one role after he was already mummy:
http://forums.carrionfields.com/dc/dcboard.php?az=show_mesg&forum=31&topic_id=54599&mesg_id=54617&page=1

Low PK count lowered base roll? Nope, Undaraxyl was far, far lower in PK count at the time, wasn't a leader, could not have had better spells and had a much higher base chance.

Colour me curious. I'm all out of ideas as to why the base roll was 20. Bug?