When first looking for an Apprentice, Stacy tried experimenting with creating a kind of cyborg-machine-marmalizer amalgamation with a person, who just so happened to be Lucy's sister Tessa (*cough* who mysteriously went missing a few years ago).
Unfortunately, since Apprentices need to be willing participants, this didn't work, and now the Creature is a reminder of a failed experiment that roams the shadows of the Ministry and haunts the park at night.
Stacy has since moved on to his actual Apprentice (design in the works) and treats the Creature more like an experiment now. A "mindless" puppet to accompany her around the Ministry and keep Advocates in check.
lan xichen is really an incredible character. his defining trait is “older brother that smiles a bit” he is a sect leader he is NOT his uncle’s favorite nephew he is canonically the hottest young master in his generation he loves to play the flute he misses his momma his best friends are both dead he ships his brother with a demonic cultivator he is an uncle he dotes on nie huaisang he recognized nie mingjue by his abs alone he was complicit if not an active participant in the deaths of his two best friends he looks like he has daddy issues he’s my silly rabbit