[RPG] Casting wall of fire in a T-shaped corridor

area-of-effectdnd-5eline-of-sightspellswall

In D&D 5e, is casting wall of fire like this allowed, or would I need to have line of sight for the entire corridor? Assume my wizard knows that the corridor extends both ways and how long it is.

Wall of Fire

Best Answer

This needs DM's approval.

Spell targeting rules prevent you from targeting a point/creature behind total cover :

To target something, you must have a clear path to it, so it can't be behind total cover. If you place an area of effect at a point that you can't see and an obstruction, such as a wall, is between you and that point, the point of origin comes into being on the near side of that obstruction.

So, you can target any point/creature in the intersection, but you can't target a point/creature in the unseen corridors (not because you don't see them - but because there's no clear path.)

Fire bolt is useless here, even if you know someone set an ambush.

Some Area of effect spells can affect creatures in the corridors, as long as there's a clear path between the creature and the spell's targeted point of origin :

A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area. To block one of these imaginary lines, an obstruction must provide total cover.

Fireball can be useful, if the ambushers are close enough : just target the intersection, and the flames will expand from there.

The wall of fire issue

The spell's description lacks reference both to "standard" spell shapes, and to a proper point of origin. Which leaves it up to the DM :

  1. He may decide the straight wall uses the "line" template - then you need clear path to one end of it. You can only affect one of the two corridors.
  2. He may decide the straight wall derives from the "cube" template - then you need clear path to a point located anywhere on a face. You can affect both corridors.
  3. He may decide you need clear path to every inch of the wall. He's the DM, after all. You can affect only the intersection.
  4. He may decide you are not targeting anything - and allow you to cast this even without any clear path or point of origin. (not likely the designer's intent). You can affect both corridors.

Option (4) may raise even more questions if the corridor is shorter than the intended wall's length. For (1) and (2), total cover from point of origin would prevent the wall from continuing after the corridor's end : but what happens when there is no point of origin... isn't described in the rules, and lies again in DM's hands.

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