Death Burst. When the eelfolk dies, it explodes in a burst of pent-up electricity. Each creature within 10 feet of it must make a DC 13 Dexterity saving throw, taking 7 (2d6) lightning damage on a failed save, or half as much on a successful one.
Hold Breath. The eelfolk can hold their breath for 1 hour.
Lunge. If the eelfolk move at least 20 feet straight toward a target and then hits with a long knife attack on the same turn, the target takes an extra 7 (2d6) piercing damage.
Electrified Body. A creature that touches the scourge or hit it with a melee attack while within 5 feet of it takes 5 (1d10) lightning damage.
Multiattack. The scourge makes three melee attacks: one with its bite and two with its claws
Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 6 (2d4 + 4) piercing damage.
Claws. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit 11 (2d6 + 4) slashing damage.
The Lunge Text reads: "If the eelfolk move at least 20 feet straight toward a target and then hits with a long knife attack on the same turn, the target takes an extra 7 (2d6) piercing damage"
I believe it should be the claws or bite and not the long knife.
This looks like a copy and paste from the basic Eelfolk stat block where that one does have a long knife attached to it.