I have a player with access to a 30' Tremorsense (because he can assume facets of an earth elemental). Tremorsense states that it senses through 'the ground'.
Just what is meant by the ground? Earth, stone, and soil? Wooden buildings? Up a tree? How would you run it?
I've had DMs tell me that critters up a tree aren't going to be sensed by it because of the ground definition and it makes sense.
Tremorsense lets the critter pinpoint the location of every creature in contact with the ground, presumably so long as the critter is also in such contact. If it is aquatic, it can do this in water too. So: Whatever way to hide the target creature uses, be it invisibility, deeper darkness or anything else, the tremorsense creature will know where it is. The way out is to fly. Whether it triggers for being in a house on the second floor is sort of unclear, though I would say it does. The type of ground doesn't matter.
Getting deeper darkness on the battlefield and having tremorsense is lovely.
Any solid surface, basically.
Spiders use Tremorsense within there webs.
I've had DMs tell me that critters up a tree aren't going to be sensed by it because of the ground definition and it makes sense.
For Tremorsense 30', all you need to do is trace 30' along any solid path. Any non-solid material between you and your target will stop this ability.
Let us say that the creature with Tremorsense 30' is 10' from a tree. On the tree is a creature, 10' up and 10' along a branch. In this scenario, the first creature would know if the second creature moved. But with no other knowledge about the tree, the first creature would not know where the second creature is. Only that it is 30' away in the direction of the tree. If the first creature knows there is a tree, it would know that the second creature is in the tree 20' from the bace of the tree. But not know where in the tree it is.