There is one drawback to this wondrous plant; it is toxic. Specifically causes 1 permanent Wisdom damage initially and 1d4 permanent Wisdom damage secondarily unless Fort saves are made (DC 15). Thus those who use it too often will be driven mad, though to the outside observer it will not be obvious that it is because of the herb and not the vision of the other side (Evil DM�s may force those who see the world of the dead to make additional saves to avoid losing their sanity, doubly punishing them).
The moss, which resembles Spanish moss except for its weak green glow at night, is hard to find as it only grows on trees used to hang people (and then only after a hundred years have passed). One dose typically costs 100 gold pieces.