SD head means Super Deformed heads....that's why in early versions of grandchase they have the so called ImBa Stats....but those which are stacked in your inventory that were first obtained in season 2 or season 1 will have normal stats in season 3......those SD heads that were obtained AFTER SEASON 3's patch will likely to have double or triple stats......that's why they're called super deformed heads....it's because of the imba stats....
***i've got the information on grandchase wiki and on this post >>