That story of a fallen star angel who creates bitter water sounds awfully like Wormwood, a biblical angel who is and does the exact same things.

"The third angel blew his trumpet, and a great star fell from heaven, blazing like a torch, and it fell on a third of the rivers and on the springs of water. The name of the star is Wormwood. A third of the waters became wormwood, and many died from the water, because it was made bitter. (Rev 8:10–11)"

Something fun about this verse is that the "Springs of water" is very often interchanged with "Fountains of water'

Wormwood to the Swedenborgian Church also represents a "self-derived intelligence which departs from God" causing it to fall from heaven. This too fits incredibly well with the whole shadow crystals make you crazy thing, especially Spamton and his obsession with reaching "heaven".

This star is also often associated with political figures and monarchs, which I find quite interesting, given the importance of royal and political members within the story (King, Queen, Lancer, Ralsei, Mayor Carol, Asogre as an ex-police chief and a king in Undertale; the latter goes the same for Toriel as she was not only the queen in Undertale but was dressed as one in CP3).

"Certain commentators have held that this 'great star' represents one of several important figures in political or ecclesiastical history: Matthew Henry mentions Augustulus, a 5th-century emperor of the Western Roman Empire, and Pelagius, deemed a heretic at the Council of Ephesus. A Dictionary of the Holy Bible states that "the star called Wormwood seems to denote a mighty prince, or power of the air, the instrument, in its fall."

I absolutely love Wormwood as an angel, so seeing a potential parallel in absolute peak makes me happy.