Melf's Acid Arrow
A shimmering green arrow streaks toward a target within range and bursts in a spray of acid. Make a ranged spell attack against the target. On a hit, the target takes 4d4 Acid damage and 2d4 Acid damage at the end of its next turn. On a miss, the arrow splashes the target with acid for half as much of the initial damage only.
Using a Higher-Level Spell Slot. The damage (both initial and later) increases by 1d4 for each spell slot level above 2.
Melf's Acid Arrow 5e 2024 vs. 2014 edition differences
Both versions are essentially the same mechanically. The 2024 version clarifies that on a miss, the splash damage is only half of the initial damage, with no additional damage at the end of the next turn. Damage increases by 1d4 per slot level above 2nd in both.