I'd personally make it a horror story. Allow me to elaborate. Make a Revenant type creature that randomly appears and chases players only to dissappear. If killed it leaves no corpse. Give it a female name and the lady of the snow body type. You could change her hue to 2301 (same hue as the death robe). This will give her the appearance and size of a girl in the age range of 8-12. I'd make her do 0 damage and give her 50 or so hp with 0 resists. That way players can kill her before they quite figured out what just happened. This would just be to set the tone.
I would also spawn her as part of a camp. Imagine this, You are running through fel, minding your buisiness, and then this pops up around you. (seen below) Just an idea. I was thinking we could do something of a murder/mystery/ghost story. Of course the big payoff would be extracting vengeance against the little girls killers. Cause thats the way reds solve problems right? We kill them.
Anyway it's coming up on 6am and I am tired. I know this is an incredibly rough version, but at 6am its all I got. If this peaks anyone's interest let me know and I will flesh this out further. If not then oh well. I'll be blue before Halloween anyway.
*side note* I think reds only want to be included, when they think you don't want them to be included. Otherwise they pretend to be too cool for the room, so to speak. Try making an announcement that reds will be barred from this event a week prior to it starting and then include them last minute. I bet they all show up.