Answers are too obvious -_-
Examples are "Guild vs. Guild Monthly Event", "Party vs. Party Event" and the "PK Player of the Month"
Other GM Events like "Hide and Seek", "RFYL(Run for your life)" and the "Cluckers/Cluck Cluck Boom" however gives away prizes less valuable than Event Hats, but more valuable than your usual items and equips
Good Luck !!