They are related to the Norse Mythology. "Ljosalf of the Nordic Alfar" is a combination of the words "light" and "álfr" (elf). These light elves are divine beings who dwell in the heavens in Álfheimr. Japanese name of "Svartalf of the Nordic Alfar", Dökkálfr, is the counterpart of Ljosalf, because it's a combination of the words "dökkr" (dark) and "álfr" (elf). Unlike the light elves who live in the heavens, the dark elves are beings who dwell down in the earth. "Dverg of the Nordic Alfar" (dwarf) and "Mara of the Nordic Alfar" (goblin) are the only "Nordic Alfar" who doesn't come from the anime and is supposed to help you to Summon "Loki". This is the second "Nordic" archetype, the first being "Nordic Beasts"; as well as now the second largest "Nordic" sub-archetype with the addition of "Mara of the Nordic Alfar".
A unique thing to note about them is that the colors of "Ljosalf", "Svartalf" and "Dverg" are cyan, magenta and yellow, respectively, while "Loki" and "Mara" are black (or shades of it). This may be a reference to the CMYK color system. Also, all of them, except "Loki", have a club-tail, similar to an Ankylosaurus.