>>19350378>and Cranidos or Shieldon>or>>19350352Extending on that post a bit, Unova has a related problem:
Rufflet requires White or White2 or friend safari
Vullaby requires Black or Black2 or friend safari
Reshiram requires Black or White2
Zekrom requires White or Black2
You can't catch all four of these by yourself unless you play at least three of the four Unova games.