So I discovered something about the Vampire Horse Whispering event while I was scrolling on Twitter. One of my mutuals posted a clip of their vampire Mii HW and I realized that the text it says is different from when my Mii does it.
His Mii would say "Darkness falls." Then, it would say "The night consumes all." Once the move is completed, the Mii would then say "Hmph."
However, when my vamp Mii does it, it says "Come, darkness!" Then, it says "Gloom, consume!" After the event is over, it says "Ha."
At first I thought this would depend on the personality of the Mii but then I remembered that I actually switched the personality of my Mii a couple of times and the text it would say is still the same so this is probably a regional difference.