It seems that you're adding every NPC that has appeared in a holiday or seasonal event to a new category. Do you think that's a necessary and/or beneficial category addition? The majority of those NPCs are already categorized under the relevant event's category.
Since many Holiday and Seasonal NPCs come and go, it's easy to forget which event they were initially a part of. I'd say when it comes to these NPCs in particular, it would be easier for a reader to find a character from a broader category rather than search through every different event that's taken place for nearly two decades. If you've been around through that many events as many of us have you're bound to forget that several even happened.
Personally, I'd been trying to do research regarding several Holiday Events I've participated in during my time playing and found it somewhat tiring to search through. However, I could understand if wanting to simply see every Holiday NPC on one page rather than search each event individually sounds lazy. I just found it much more efficient, especially when trying to remember who certain NPCs were and not being able to remember the year their event happened.
I appreciate your reasoning and agree with you. There's already a Category:Quest NPCs category that was likely created for similar reasons. I definitely can't remember the details of many of the holiday/seasonal events, never mind the NPCs involved in some of those events.
I do think that the category should be plural, as with the Quest NPCs category mentioned above. I wonder if a more appropriate category would be 'Event NPCs'. If the category is 'Event NPCs', it may make sense to include NPCs from time-limited events and such, as well as the usual holiday/seasonal events. I'm very interested in what you think.