Shimmer saw - experienced - that whump and raised it an, "Oof!" Not being the tallest woman in the world, it resulted in a crumpled heap of something which may or may not even be actual clothing, considering what Derek had recently witnessed.
Which was also part of the reason for the illusionary figure to peer out of her curtain of dark hair and give a sudden wide-eyed yelp, flapping her arms as if it would allow her the ability of powered flight, before settling on the strategy of speedy backwards shuffling. It was like someone trying to do an impression of a mobile tree stump.
Vampire horse guy...
Awkwardly getting to feet, Shimmer looked on with open-mouthed fascination, looking him up and down and seeming, for all the world, as though she was about to grab a pitchfork and encourage the town to burn him alive - before, all of a sudden, giving a note of laughter and smile in realisation of what this meant.
"Dude! You should've told me! I mean... You couldn't, 'cause... Big ole' secret and Grr! But I can get you all the best capes! A-a-and I know this guy who's trying to offload these coffins and I can get you cut-price! What are you even doing here?!"