You all remember Ghost Invasion that appear on server only at Halloween. And I find it strange that this game haven’t got max costume (like Humbug and Groundhog).
Reward for 20 level in this game is - Spooperhero Hub Title. My idea make this hub title unlockable at level 19, and new reward for 20 level is - Exclusive GI costume! I think it pretty awesome, because other Limited Time Games (Snow/Ground Wars) have Max level costume!
UPDATED: If admins think this unbalanced way to get costume, they can increase level cap or make XP level up slower (like Ground Wars)