Sorry for the delay. I thought I'd already replied to this.

There isn't any physical representation of the animal beyond the mark. It's simply something to represent them.

The mark only appears on the tree, yes. And it'll show up in a place that isn't being watched.

The animals can be anything from any world, living or dead, real or not.

When characters wake up, they'll wake up with the same items they first arrived with. Anything else they've found since first arriving will still be in their previous homes, but can be reclaimed.