Based (loosely) on the WoW cloud serpent.

The lightning serpents (or lightning hawks, thunderhawks, or cloud serpents) are a family of winged serpents found in the badlands, canyon-lands, savanna, and desert, capable of generating a powerful electric shock to subdue prey.  These creatures feature feathery wings and plumage ranging from blue to white in color, and are usually seen hovering, supernaturally suspended on slow-moving wings, or streaming in cartwheels or figure-eights in the air.

Lightning Serpent

Small beast, unaligned

Armor Class

12

Hit Points

14 (4d6)

Speed

10 ft., fly 60 ft.

STR	DEX	CON	INT	WIS	CHA
8 (-1)	14 (+2)	10 (+0)	2 (-4)	13 (+1)	3 (-4)

Skills

Perception +3, Stealth +3

Damage Immunities

lightning

Senses

passive Perception 13

Languages

—

Challenge

1/4 (50 XP)

Discharge.

When the lightning serpent strikes a creature that has been polarized with its bite attack, it releases electrical energy into the target, ending the condition. The creature must make a DC 11 Constitution saving throw (with disadvantage if wearing metal armor), taking 2d6 lightning damage and becoming stunned until the end of its next turn on a failed save. On a successful save it takes half as much damage and is not stunned.

Keen Sight.

The lightning serpent has advantage on wisdom (perception) checks that rely on sight.

Actions

Bite.

Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 3 (1d4+1) piercing damage, and discharge if the creature was polarized.

Polarize.

The lightning serpent targets one creature it can see within 40 ft. of it, causing it to become polarized. The creature is aware it is polarized (hair standing on end, etc.) but it does not necessarily know what this effect does, nor the cause of it. This effect ends at the end of the lightning serpent's next turn, if the creature is affected by discharge or if the creature drops is able to touch an object made of metal that is in contact with the ground.

Combat and Tactics
Lightning serpent in the wild are communal creatures, engaging in combat either to obtain food or to defend their roosts from intruders. In either case the lightning serpent prefers to attack from above, opening with polarize and then diving to bite its target, using the stun effect of discharge to prevent counterattacks when it flies out of reach. If possible, a group of these serpents will fight together, taking turns polarizing and attacking the target to keep it stunned- they are aware that they are easily slain and prefer not to fight without this advantage. Unless lacking for food, lightning serpents would only engage in combat with a group of humanoids if their nest was threatened.
Animals living in the territory of a nest of lightning serpents are usually well aware of what the sensation of polarized means and will attempt to flee when affected by it, while sapient beings know to take cover, ground themselves, or guard themselves until the effect fades.

Ecology and Lore
Lightning serpents of all kinds tend to live in nests far from the ground, either near the top of steep cliffs in rocky terrain, or in treetops. A roost might contain up to eight adults, and many young (as their survival rate is fairly low). These creatures hunt in groups of up to perhaps half the roost, preferring large prey relative to their size (Medium-sized creatures, mostly) as they feed only rarely. In a group, they are well equipped to take down a larger creature if it's alone, but once they have their quarry they are unable to return it to their nest whole: they make multiple trips to bring meat back for the young, those that didn't hunt, and to gorge themselves on. Consequently, scavengers are often found near lightning serpent nests, able to find consistent food from the remains of their kills (with little danger once the serpents have abandoned the remainder).

To generate their electrical magic, the serpents need to consume small amounts of certain metals. Some of the serpents' time is thus spent pecking and scraping with their hard beaks and claws at ore-containing rocks for small flakes of metal, which they consume. The serpents are able to detect iron and copper in rock that would otherwise be invisible, leading some prospectors to follow the creatures from a distance for leads. When well-trained, a lightning serpent can be taught to identify gold and silver as well (though they have to be bred specially to be docile enough to keep as a pet).