If we get one more Hero then December will tie with May for the highest monthly total (33) and it will also tie with March, April and August for the highest number of new Heroes in a month (18).
Would need two more costumes to tie the monthly costume count with the leader, which is May on 17.
Maybe something for Valhalla tomorrow ? 
EDIT TO ADD:
Just checked our Resident Oracle’s predictions.
Looks like a silver medal for December. 