Subtle spell and saving throws

Question

I have a rules question about the Subtle spell metamagic option.

My sorcerer has just learned the Fireball spell and tries to cast it spending a sorcery point as subtle spell. If the enemy can't hear or see the caster casting the spell, can they make a Dex saving throw? Or they auto-fail; considering that they will see just the visual at the last minute (almost as if they are in "blinded" condition)?

To take it one step further, if they can't see the caster casting, what about Wis or Int saving throws?

Answer 1

While spell attacks are affected by the unseen attackers rule (PHB 194) as any other attack, saving throws follow different rules. In the general rules for saving throws we read that:

A saving throw can be modified by a situational bonus or penalty and can be affected by advantage and disadvantage, as determined by the DM. (PHB 179)

But while it is left up to the DM, there is also the arcane trickster feature magical ambush:

if you are hidden from a creature when you cast a spell on it, the creature has disadvantage on any saving throw it makes against the spell this turn. (PHB 98)

It is strongly implied that this is a special rule overwriting the general case. Granting this to all characters (and NPC-s) would make this feature redundant.

There are not many features that grant disadvantage on saving throws. The above rogue feature is acquired on level 9, and the sorcerer metamagic that does it is generally the most the expensive one. It is clear that such a thing should be regarded as really powerful. Consider that traps also grant a saving throw as normal, even though they need no components to cast and are usually hidden.

Thus I advise against ruling that being hidden should grant disadvantage on saving throws.

Answer 2

No, the enemy makes their saving throws as normal. You say that they can't see or hear you casting the spell; this is equivalent to them being blind and deaf. So let's look at an enemy who is actually blind and deaf:

Blinded

• A blinded creature can’t see and automatically fails any ability check that requires sight.
• Attack rolls against the creature have advantage, and the creature’s attack rolls have disadvantage.

Deafened

• A deafened creature can’t hear and automatically fails any ability check that requires hearing.

Being blind and deaf has no effect whatsoever on a creature's saving throws, so Subtle Spell shouldn't either.

Answer 3

RAW, Subtle Spell does not affect saving throws, so the targets would get their normal saves.

I do like to encourage creative solutions, without making that overpowered, so I would consider giving the caster some advantage, if he described his course of action well to gain this. At best, then, I would treat this similarly to being surprised -- that is, if this is the opening act of hostility, and the Subtle Spell is used to start the fight without any warning, then I as the DM would consider giving the targets a disadvantage on that first save, while they are still effectively surprised. Once combat has been joined, and the targets no longer surprised, subtle spell would no longer be relevant for this; it's only real use would be to perhaps make the enemies unsure of which character is the spellcaster.

Answer 4

Subtl spell doesn't change the saving throw to avoid your fireball, but as often the case with 5e usually stuff such as this are up to the DM to make a ruling, usually in the form of advantage or disadvantage. With the target being unawares I would rule that the target has disadvantage.