Shortly after the closed beta of this game monster spawns were done by gm's, and was also done in aura kingdom. Grand fantasia also had weekly monster spawns which gave the players a lot of enjoyment. So my idea is basically working out a time period that works within the GM's or CM's free time to do weekly monster spawns. The bosses used could be a range from normal trial bosses on mass spawn, normal holiday event bosses to bosses like the 25 man dungeon boss Borsey.
The rewards would be simple drops and achievement completion for players who haven't done them before or were absent during their introduction to the game.