If Weave Together the Fabric of Place joins lands on two adjacent boards, what happens if you destroy one of those boards with Cast Down Into the Briny Deep?
If Weave Together the Fabric of Place joins lands on two adjacent boards, what happens if you destroy one of those boards with Cast Down Into the Briny Deep?
It will destroy everything in the joined land, since it's on the board being Cast Down. (The land is on both boards.) If you target the conjoined land, you choose which single board to sink.
If you want (player option) and you have a convenient item handy to mark a land as "destroyed, no longer exists", then Cast Down Into the Briny Deep will also destroy lands that are normally on other boards but were part of the destroyed board at the time of its destruction. (If this splits a board in two, lands on one side of the gap are considered Range 2 from lands on the other side.) But if you don't want to do this, or have no convenient way of marking the land as obliterated, it survives. Also, you can't do this for the Ocean, even if Oceans are in play.
