How often does Ferumbras appear in each world?

Question

I'd like to know how many times Ferumbras appear on each world in a year? His respawn is fix or it might vary?

Answer 1

it is around every 6 months exept for the first one in each server ( still happen between the first 6 months)

Answer 2

Ferumbras appears twice a year on each server.
His spawn might vary for some days.

I recommend checking out www.tibiabosses.com if you want to know when will be next respawn of Ferumbras. 

Answer 3

Time of respawn takes about 170-190 days. It's easy to count this range in case of smaller bosses which appear more often, but Ferumbras has quite long time of resp.