The night would begin as normal, Mumbo faking his role as a butler and Lizzie as a mystery aristocrat. Deeper into the night, Lizzie would have succesfully spread rumors of there being "A Vampire Butler" to catch the attention of the hunter, describing this butler to "Have a very fashionable mustache" and a "bat-like mask". After these rumors reach the man, he asks specifically for that butler to bring him a drink, a drink that lizzie had poisoned beforehand with a slow-acting poison so he'd be able to drink other things by the time it hit him. Once Mumbo had delivered the drink, and succesfully hid his vampirism, the two of them would quickly flee the scene before any of them would realize that the aristocrat had been poisoned.

With enough time between the aristocrat drinking the poison, and them actually dying, Mumbo and Lizzie would have enough time to frame whoever brought him a drink next, succesfully escaping.

The two of them would hunt the hunters that went after those like them, and sometimes meet up with other less than trustable people that could give them favors and the like in exchange for their services. If I could write I would also do something with the idea of the watchers being a weird cult, what if the people they went after were also avid followers, so Lizzie and Mumbo ended up catching the attention of the wrong type of deities for all the wrong reasons and ended up having to fight against them? (Not necessarily a flashy physical battle, maybe simply not succumbing to hallucinations or voices that these watchers give them and so on and so forth)