In the Update following the Nightmare Night video, the tumblr received an influx of asks related to Fluffle's sister. What the 9 panels of the response showed were:

She's not biologically Fluffle Puff's sister (No big surprise...)

She can speak telepathically

She uses "we" instead of "I"

She genuinely seems to care about Fluffle Puff, who she calls "Little One"

And her name... Well, while Fluffle calls her "Big Sister..."

I love "Marksaline the Necromorph Queen," because that's a direct Shout Out to Adventure Time.

So fluffle officially loves and incorporates: dead space, adventure time, dan, and house into the universe.

Yeay Star!

Oh dear, this is going to be interesting...

3765712 I don't understand.

3825810

It's a reference to Marceline the Vampire Queen.

3825924 Oh... I don't watch Adventure Time, so I wouldn't have gotten it if you hadn't shown me that.