The last actinide goes to the last new pony to appear in the entire series. Luster Dawn’s name also contains both the former (Lw) and current chemical symbols for lawrencium, and suggests light and the “luminosity” that is one parameter of the cyclotron which Ernest Lawrence invented.
I was gonna make the joke but you beat me to it by at least a day.
@Background Pony #46A4
Her name contains the letters L and R.