Board Thread:General Discussion/@comment-6192846-20150419144803/@comment-4698889-20150603044137

Continuing this space tangent, the way the Yards work resembles how a planet is stuck between two larger planets of great but equal gravitational force (hence the pull). Once the Third Period was destroyed, the Hellish Yard gained power, sort of like how a planet gains mass and thus gravity. And since there was so much gravity, the Hellish Yard managed to pull both the Third Period and the souls of the dead into itself, causing a collision (a.k.a. "merge" of the two).