Then I thought about it, and I decided that there were really two options if I allowed it to happen. I could either have the player foresee a place so terrible that the party would never willingly go there, or reveal an intriguing location that would strongly tempt the party to open a portal and travel there.
As for option 1, I want to keep all the truly horrifying locations (we have arrived at the 666th layer of the Abyss, local time is 6:66, temperature outside the portal is 451 degrees Fahrenheit, thanks for flying Plane Shift...) in reserve for the time the party decides that whatever lies on the other side of a random portal has to be better than the current situation they are in. So that is a no go. What good does describing a wicked awesome and dangerous place do if the party would never, ever, willingly go there?
As for option 2, this sounded good to me. As it is, the Plane Shift mutation has only been used once in play and the party has never actually gone through a portal. So why not encourage a little planar hopping with a tempting vision of the future?
This is exactly what happened last session. This is what awaited on the other side of the precogged planeshift:
As I mentioned in a post over at my other blog, this is a crappy, low-res pic I took with my old cell phone of one of my drawings.
I described the ground and landscape as some kind of fleshy purple substance, I told the group that the eyes of the faces in the hillsides were slowly blinking, and I described the fight between the shiny knight and the dragon. After assisting the knight defeat the dragon (in the vision of the future), the knight lifted his visor and revealed himself to be some sort of faerie or elf. He spoke in a melodic and silvery tongue that was, of course, incomprensible, but then he pointed behind him to a castle in the middle of a lake, surrounded by a normal forest.
The party is very excited to go on a dragon slaying expedition and are dreaming big about bringing back piles of dragon parts to assist the Mice of Camelot in making some mech suits for the party. Dragon-scale mechs, anyone?