Reserving a Litwick for Arceustar.
Arceustar, you get Two Paths the Litwick. This Litwick is both Ghost and Fire, meaning it must choose which path to follow. Whatever path you choose for it, it must take that path and becomes your Fire or Ghost.
Path of Fire:
-Evolve after soloing Brycen.
-No Ghost-type moves.
-Must know two damaging Fire-type moves ASAP.
-Must not know Will-O-Wisp, as that is also considered part-Ghost.
Path of Ghosts:
-Evolve whenever.
-Solo Marshal or Caitlin of the E4.
-Solo N's Reshiram, as Ghosts are dark, whereas Reshiram is white.
-Must have 2 damaging Ghost-type STAB ASAP.
-Must not know any Fire-type moves.
-May not be used against Brycen.
No matter what path you take, after the Elite Four, N, and Ghestis, Lampent realizes that its true destiny lies as a dual-typed Pokemon. Before evolving into Chandelure, the two paths merge. You must now know a Ghost move and a Fire move, must know Will-O-Wisp, which represents a blend of the two typings, and then solo Cynthia's Spiritomb to evolve.
I choose fire