Syndra is the second dark themed Ionian Champion, along with Varus and Zed. Only Varus And Aatrox shares a light/divine themed skin.
Syndra's dance is based on the choreography for the song Hoot by Girls' Generation (소녀시대: So Nyeo Shi Dae), a popular Korean girl group. A side-by-side comparison video can be seen here.
Syndra is the second champion that dances to one of the group's songs, the first being Ahri.
Syndra is the third champion to currently have a difficulty rating of 100, the first being Cassiopeia and the second being Orianna. On release, her difficulty rating was originally 90.
Each of Syndra's abilities gain new graphical details when levelled to max rank. Dark Sphere gains a darker shockwave color (red for Classic skin, orange-gold for Justicar) and cracks the earth; Force of Will gains a similarily-colored, larger shockwave as well as an energy trail following thrown spheres; Scatter the weak gains a similarily-colored energy wave and electrical jolts; when attaining the max rank of Unleashed Power, the three orbs floating around Syndra will have a slight change of appearance and will leave a trail.
Syndra is the second champion speculated to be omnipotent, or nearly so. The first one was Xerath.
Her helm also looks similar to a "Mantle of Decorum", Ionia's highest decoration. However, it is placed on her forehead instead of floating behind her head, as a sort of symbol of power, much like a crown.
Justicar Syndra is possibly what Syndra would look like if she were not evil and embraced the Ionian elders' teachings instead of being restrained by them. This assumption has basement in the yellow spheres, warm color scheme and the use of white feathers. Her spheres and helmet also resemble the sun which is also a symbol for divinity.
The word "Justicar" also means "man of justice" i.e a judge.
It is also the first light themed skin for a dark themed champion. The other being Arclight Varus.
The primary play on words is regarding her lore where she was deemed mentally unbalanced by her Ionian elders (as balance is a defining virtue in Ionian culture), and stands upon on her dark spheres to prove that she "has balance."
It also refers to Syndra's champion balance as she was reportedly overpowered during development.