Kirwan was described as being tall. He had slanting eyebrows and long, flaming red hair that tumbled over his shoulders. His eyes were brilliant green. His skin and eyes could change colour to match his surroundings, however his true eye colour, like other Fellan, was brilliant green.
Kirwan, like other Fellan, had magic. He had the power to tame beasts of the Fellan realm, change shape at will, move from place to place in a breath, speak to other Fellan through his mind an many other wonders that includes controlling the wind and presumably other elements of the Fell Zone forest.