How to resolve Burning Hands with a Dying Ally

Question

Playing the D&D 5e starter set, the rogue had been knocked prone by the wolves in the Goblin Cave and had two wolves within melee range over her 0hp body.

I ruled that, as she was prone, the wizard could direct Burning Hands above her to just hit the wolves. But if I hadn't, my assumption would be that the rogue could not make a Dex save (because dying) and would automatically fail a death save.

I was interested in what the actual rulings about using that spell with dying allies in the area of effect are?

Answer 1

The rogue fails a saving throw (unless sculpt spells is used)

You are right: being unconscious / 0 HP is an auto-fail on Dexterity saves, if a save needed.

Unconscious (relevant point)

• The creature automatically fails Strength and Dexterity saving throws.
  (PHB, Appendix A, Conditions)

You are correct on the failed death save. (If damage is done).

Damage at 0 Hit Points.
If you take any damage while you have 0 hit points, you suffer a death saving throw failure. If the damage is from a critical hit, you suffer two failures instead. If the damage equals or exceeds your hit point maximum, you suffer instant death (Basic Rules, p. 76, Death Saving Throws)

But would damage have been done? Probably not.

Your ruling fits the spell's shape.

I like your ruling¹. This kind of judgment call is what can add a lot of fun to a gaming session. Given the spell description, I'd say you were well within the rules. (See below).

As you hold your hands with thumbs touching and fingers spread, a thin sheet of flames shoots forth from your outstretched fingertips.

Further that point, if the wizard is from the Evocation School, and 2d level or higher, the "sculpt spell" feature would have allowed zero damage to happen to her even if she was in the area of effect.

School of Evocation
Sculpt Spells
Beginning at 2nd level, you can create pockets of relative safety within the effects of your evocation spells. When you cast an evocation spell that affects other creatures that you can see, you can choose a number of them equal to 1 + the spell’s level. The chosen creatures automatically succeed on their saving throws against the spell, and they take no damage if they would normally take half damage on a successful save. (Basic Rules, p. 32).

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¹Taking into account the shape of the spell: a cone.

If you look at the spell description, Burning Hands is a cone.

Burning Hands; 1st-level evocation; Casting Time: 1 action; Range: Self (15-foot cone); Components: V, S; Duration: Instantaneous

It is easy to argue that it is aimable in the Z-axis as well as in the the X and Y axes. If you adjust it as a caster, the wizard could aim the cone in such a way as to miss the prone Rogue and still hit the wolves. Your judgment call accommodated that spell shape without getting too much into simulation. Depending on what you judge as the degree of difficulty in so aiming, you may or may not wish to grant advantage to the saving throw the wolves make. (Thanks to @SeraphsWrath for raising this point)

That said, the spell's description and area of effect is a little unclear.(Cone, Basic Rules, p. 80)

As you hold your hands with thumbs touching and fingers spread, a thin sheet of flames shoots forth from your outstretched fingertips. Each creature in a 15-foot cone must make a Dexterity saving throw

So what is it? A cone or a thin sheet of flames? Since "sheet and cone" are both used in the spell description, the text is unclear and so we addressed this in detail in a different question. @Yakk points out that "a cone whose surface is a thin sheet of flames, but whose interior is empty, matches both descriptions used in the spell."

Answer 2

It depends on the dimensions of the characters

In 5e, areas of effect do not snap to a grid by default. As such, the cone area would move out from the caster's hands and may not hit the prone character.

A cone's width at a given point along its length is equal to that point's distance from the point of origin.

This means that a creature is only affected by the spell if at any point the horizontal distance to any part of the creature's body is greater than the vertical distance to the caster's outstretched hands. A gnome wizard would almost certainly hit the prone character while a elf might not.

Angles

Additionally, it is possible to angle a cone effect so that the lowest point of the cone lies on a flat plane.

A cone extends in a direction you choose from its point of origin

[emphasis mine]

This means that even the gnome wizard could avoid hitting his/her ally.

Because this is an option, allowing the caster to "aim" the cone, as you did, is a perfectly sound ruling

Answer 3

I would say that the wizard could use burning hands above her, however this could also provoke the wolves into ripping their chains out of the ground and either (a) killing her or (b) attacking the wizard based on where he is. This result is supported by the quote in section 3:

If the wolves are goaded by enemies beyond their reach, they are driven into a frenzy that allows them to yank the iron rod securing their chains out of the floor. Each round that any character remains in sight, the wolves attempt a single DC 15 Strength check. On the first success, they loosen the rod and the DC drops to 10. On a second success, they yank the rod loose, bending it so that their chains are freed.