TBH, I don't understand the element system at this point. But I noticed some interesting things about the pairings:
Some of them really seem to go together. For instance, thunder/light- well, thunder and lightning, although "light" in this instance probably does not meant lightning, just light itself.
Death/scythe, while used for Jevil, also makes me think of the Grim Reaper and his scythe. Reaper Bird, anyone? And if you think it's weird that I'm bringing up an amalgamate at this point, remember that elec/holy is another element pairing. In Undertale, the only time "electrical attacks" is mentioned as an element is for Shyren, and it was Shyren's sister (apparently named Shyra, according to the headstone in the Hometown graveyard) who was turned into another amalgamate, namely Lemon Bread. Long stretch, possibly unfounded, possibly wrong, but worth noting anyway, I think.
As for dark/star, I felt like I'd heard that phrase before (and no, not the movie, I'd never heard of a movie called "Dark Star" until I googled the phrase), and found this in Webster's Dictionary:
"Invisible but luminous" and "causes a primary eclipse"- why am I reminded of "eyes blinded by darkness"?