I forget if I suggested this before but if I have.. I guess I'm doing it again! 8U
heRO has had a LOT of unique seasonal/special events that gave out/sold tons of custom holiday gears, but getting your hands on something specific if you missed out is almost impossible.
What I'm suggesting is a new feature to the Timeless Room, wherein players could speak with an NPC and travel through a time rift to a special iteration of Prontera (featuring an appearance of the special maps/NPC's we've had over the years, spring/winter/fall/valentine's/halloween/summer/whatever-else-we've-had) and turn in items + zeny to Pandelina/Anabelle/etc to obtain a specific holiday/birthday gear that they missed out on getting. This could also serve as a means to choose a feature for a stylish hero cap to make it useful, for players who weren't here 2 years ago to get a hax hat, or didn't have certain characters yet at the time.
Players could be limited to 1 time-travel visit & choice of buying 1 gear, and would have to do the Zodiac Gate Quest to allow access to the Timeless Room each time.
Potentially OP? Not sure, but I think it'd be pretty awesome