Does anyone have any ideas for the advancement and the built that that the formidable pyreen should have?

Number in levels or ability scores?

I am in the quest of creating him in accordance to what the timeline of Athas mentions but I need all the help I can get.

Is there any official source where I can find any statistics of him or any line even implying a power with its roots in the system?

from what i understand the pyreen are a composite race. an experiment of the early halfings. i use a home brew system that i allow PCs to play a pyreen. the pyreen race can level in any class. the actual racial traits are derived from a table that has all the races in your ds campaign. i made it easy and simply used ten races. simple roll the ten sided die four or five times to get an amalgam of races that is the pyreen. then take the best scores from each race kinda like a gestalt character. slap a +1 level adjustment on her and your good to go.