Acid Splash 2e FAQ FAQ
Does Acid Splash require an attack roll in AD&D 2e?
No. The D&D Portal 2e conversion does not use THAC0, Armor Class, or a missile attack roll. The primary target makes a saving throw vs. spell; on a failed save it takes 1d4 acid damage, and on a successful save it takes none. Creatures caught by the 3-foot splash also make their own saving throws vs. spell, taking 1 acid damage only if they fail.
Later and contemporary AD&D spells use several different ways to resolve offensive magic, so an acid projectile does not automatically imply a weapon-style attack roll. D&D Portal deliberately chose the saving-throw route for this conversion. That keeps a very small 1st-level spell from requiring an attack roll and then additional defensive rolls for a tiny amount of damage.
The primary target makes a saving throw vs. spell
After Acid 
D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash is cast at a creature within 30 yards, the caster does not roll to hit. The selected creature instead makes a saving throw 
D&D Portal - Saving Throw D20 test rule Saving Throw is a d20 test rule used to resolve
uncertain outcomes during play. Full link: https://dnd-portal.com/rules/d20-tests/saving-throw/ vs. spell.
A failed save causes 1d4 Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/. A successful save negates the damage completely.
Because there is no attack roll, the target's armor class 
D&D Portal - Armor Class Combat rule Armor Class is a combat rule used by attacks,
damage, defenses, or turn order. Full link: https://dnd-portal.com/rules/combat/armor-class/ and the caster's THAC0 do not determine whether the primary Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ occurs.
Nearby creatures save separately
Other creatures within 3 feet of the primary target are exposed to the minor splash rather than the main 1d4 damage.
Each of those creatures makes an individual saving throw D&D Portal - Saving Throw D20 test rule Saving Throw is a d20 test rule used to resolve
uncertain outcomes during play. Full link: https://dnd-portal.com/rules/d20-tests/saving-throw/ vs. spell. A failed save deals 1 point of Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/, while success prevents it.
The primary target's save does not control the nearby creatures. Different creatures can therefore have different outcomes from the same casting.
Why the conversion uses a saving throw
The 3e Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash uses a ranged touch attack, but AD&D 2e has no directly equivalent touch-AC mechanic to preserve.
Using a save vs. spell gives the target an edition-native defense and avoids creating a special miniature attack subsystem solely for Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash.
It also differentiates the conversion from spells such as Melf's Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Arrow, which already occupy the projectile attack-roll space in 2e.
Magic resistance is a separate defense
A creature with AD&D 2e magic resistance can use that defense when Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash would directly affect it, following the normal magic-resistance rules.
If magic resistance negates the spell for that creature, the spell has no effect on it. If the resistance does not negate the spell, the creature still receives the saving throw D&D Portal - Saving Throw D20 test rule Saving Throw is a d20 test rule used to resolve
uncertain outcomes during play. Full link: https://dnd-portal.com/rules/d20-tests/saving-throw/ vs. spell allowed by Acid D&D Portal - Acid Damage type Acid is a damage type used by attacks,
spells, class features, resistance, immunity, and vulnerability. Full link: https://dnd-portal.com/rules/damage-types/acid/ Splash.
Magic resistance and the saving throw D&D Portal - Saving Throw D20 test rule Saving Throw is a d20 test rule used to resolve
uncertain outcomes during play. Full link: https://dnd-portal.com/rules/d20-tests/saving-throw/ are therefore separate defensive layers. The conversion does not replace one with the other.