As you are currently looking for events in game why not offer a monthly festivity surrounding the name of each month, Each month offering a small bonus. ie
January
from Janus, god of beginnings and transitions ( doors, endings of time. Janus god proceded over war and peace - possible boost could be combat related and would require daily login and exchange of player coin ( or donuts for better boost) like an offering for more PVP or ability to mask remove self from PVP...Increased counter attacks?
February
( festivity ) from latin meaning purify, which had a ritual act to wash and clean. This would be easy and offer player increased use of washing machine.
March
Roman god or war Mars, and we return to a PVP boost, this time I would suggest a boost strength stat ( non permanent, with option to buy with donuts strength stats directly, as strength is one of most unused stats this may make game more interesting ie more failed hard missions greater success in team wars.
April
aprilis celebration of festival to farmers, growers this month would be a good month for a donut sale to reflect this and it was also month which would celebrate Aphrodite , perhaps a boost to intuition to reflect this? ie term ' female intuition'
May
from maiesta honour and reverence, this is an easy one... I'd suggest offering either honour boost or copying in style of january
June
Juno (not the film) fro root of junior ie youth, perhaps a energy boost to players below level 50, this would encourage new players in this time frame. May be a good time to also implement a reward system with a real world or donut prize ie gain so much ( honour xp etc or some game or gadget) ran from sites the game is ported through.
July
named after Julius ceasar, I'd suggest repeating earlier PVP or perhaps alter to XP related thus idea of being ruler over others with highest level.
August
Sextus=six, which later became named after augustus. Augustus whose life offers you any form of celebration from I'd suggest a coin boost from PVP. With a month long competition over honour, give winner item, coin, donuts.
September
7
October
8
November
9
Decemer
10
For numerical rotate the pvp xp gain, each month boosting stats by that figure temporarily.
While the roman theme works for English namings, most cultures have a historical value or root thus this theme could be replicated in other servers or you could create your own theme a possible vehicle you could use would be following prolonged manufacture to of the perfect donut recipe.