Spark Mephit A5E

Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) slashing damage plus 2 (1d4) lightning damage.

The mephit transforms into an arc of lightning and flies up to 20 feet without provoking opportunity attacks. During this movement the mephit can pass through other creatures spaces. Whenever it moves through another creatures space for the first time during this movement that creature makes a DC 12 Dexterity saving throw taking 5 (2d4) lightning damage on a failed save or half damage on a success. The mephit then reverts to its original form.

Each creature within 10 feet of the mephit makes a DC 11 Dexterity saving throw. On a failure the creature is magically outlined in blue light for 1 minute. While outlined the creature gains no benefit from being invisible and attack rolls against it are made with advantage.