Can you use Twinned Spell on Fireball and target the same creature with both attacks? [duplicate]

Question

Can a sorcerer use the Twinned Spell metamagic on the fireball spell and target the same creature with both attacks?

Also, if you can target one with both, would it be double damage?

Answer 1

No, for two reasons.

Twinned Spell can't be used with fireball

The sorcerer's Twinned Spell metamagic option has some restrictions on what spells it can be used with:

When you cast a spell that targets only one creature and doesn’t have a range of self, you can spend a number of sorcery points equal to the spell’s level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip).

To be eligible, a spell must be incapable of targeting more than one creature at the spell’s current level. For example, magic missile and scorching ray aren’t eligible, but ray of frost and chromatic orb are.

The description of the fireball spell says:

A bright streak flashes from your pointing finger to a point you choose within range and then blossoms with a low roar into an explosion of flame. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 8d6 fire damage on a failed save, or half as much damage on a successful one.

By definition, all area-of-effect spells (that I know of) are able to affect more than a single creature. Thus, AoE spells, including fireball can't generally be twinned.

(It's not just about whether the spell does target more than one creature; it's about whether the spell is capable of targeting more than one creature. Fireball is capable of targeting any number of creatures within its area of effect.)

A Twinned Spell has to target two different creatures

As quoted above, from the description of Twinned Spell:

When you cast a spell that targets only one creature and doesn’t have a range of self, you can spend a number of sorcery points equal to the spell’s level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip).

Jeremy Crawford, official rules designer for 5e, confirms this on Twitter:

Hey, can twinned spell, target the same person twice?

If a rule, such as Twinned Spell, says you affect one creature and then a second creature, those are two different creatures.

Even if you could twin fireball, or no matter what other valid spell you use Twinned Spell on, you need to target two different creatures with the two instances of the spell. You can't target the same creature twice with a Twinned Spell.

A minor note: fireball isn't an "attack"

The basic rules define attacks very simply:

If there's ever any question whether something you're doing counts as an attack, the rule is simple: if you're making an attack roll, you're making an attack.

This includes both melee and ranged attacks, and both weapon and spell attacks. The only addition is that grapples and shoves are described as "special melee attacks", even though they don't involve an attack roll. So something is only an attack if it involves an attack roll or if it is specifically described as an "attack".

Fireball doesn't involve an attack roll, and it's not described as an attack. It merely requires any affected foes to make a Dexterity saving throw to potentially halve the damage. As such, fireball is not an attack.

See this question for more details: Do saving throw based spells that do damage count as attacks?

Answer 2

No, you can't.

Twinned Spell:

When you cast a spell that targets only one creature and doesn't have a range of self, you can spend a number of sorcery points equal to the spell's level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip).

As I emphasized, the twinned spell must be a spell that targets only one creature and not an area spell like fireball.