If you ever grow tired of your Tree-Hugging Vampires, you can always resign from the event, rejoin, or maybe give those "rainbow" lands a whirl
At first, this looks like a much, much worse Ghostly Prison, in that it doesn't actually stop attackers
It does require tapping, so you'll need to wait a turn to use it normally, but you can easily combine it with Commander Classics Swiftfoot Boots and Lightning Greaves to protect it and haste it in one swing
For example, if you somehow used Souls of the Lost to craft Mastercraft Raptor (perhaps because it became a copy of a Dinosaur), its power while in exile is equal to the number of permanent cards in your graveyard, and Mastercraft Raptor's power will change as the number of permanent cards in your graveyard changes