Suppose a wizard casts Teleportation Circle (or Plane Shift) and writes down a sigil sequence not corresponding to any circle the wizard knows. We're not concerned with why they would do this; maybe they made a mistake, or they just want to travel. What would happen to this wizard?
The possibilities I can think of are:
- The spell fails, consuming a slot but nothing happens.
- The wizard teleports to the circle bearing that sigil sequence, if it exists, even though this circle was not known to the wizard before casting the spell. If it does not exist, a mishap occurs as in the Teleport spell when aiming for a false destination.
- A mishap occurs even if there exists a circle with that sequence.
If there's a RAW way to resolve this, I would guess it says #1, but as a DM I'd be inclined to rule toward #2 just to be interesting. There are a lot of teleportation circles out there in the multiverse, and I find it hard to believe the spell "knows" whether you know a circle or not, so writing sigils at random seems like it should at least take you somewhere. Especially if you use Plane Shift so it's not limited to only the plane you're currently on.
Is there actually an established procedure for this? If not, what is the best way to make this ruling, as backed up by experience?