Gesthari

In the far northern oceans, the where the ships no longer travel, where the perpetual storms roam, live the Gesthari.
Wraithlike creatures, beautiful and deadly, they inhabit the clouds, feeding from the lightning. They will swoop to the ocean to strike down to draw a wayward sea creature into their tendrils.

The Gesthari reminds one of the jellyfish, and it's tendrils are far more dangerous, striking a creature with deadly poison and burning agony. Though they are a species with two genders, they possess a duality within themselves of male and female. The female aspect is impregnated early in life and will continue to lay the eggs of that joining for it's entire life, which is up to 80 years, some say.

Eggs are laid in the bodies of their corpses, and they will mark these corpses with a scent to let others of their kind know it is not for eating. The young hatch quickly, devouring all flesh and making their way quickly into the sky. They are the reason that ships attacked in such a manner are found full of nothing but bones. The young, once skyborne, will mate and remain skybound for two years, at which point they are fully grown.

They are not that large at full size, merely the size of medium sized dog. However, their tendrils, when dropped, will conspire to make them appear much larger.

The Gesthari are not an intelligent species, although they do possess a sub-intelligence capable of letting them use simple tools and open doors, a trick they learnt long ago, but they drift in groups, coincidentally known as a Drift of Gesthari.
They seek out schools of fish and will descend upon them, feeding and spawning. By an unknown means, the Gesthari are capable of moving around in all directions unhindered, leading to a distinct, and correct, otherworldly feel to them.

Usually of no trouble to anyone, they become a danger during storms for a ship crossing the Northern seas. Given to seek out life, they will descend upon the ships and devour and spawn within the hapless travellers. They are not particularly strong physically, and may be killed with no more than a sturdy blow to their main body, but it is in their poisonous tendrils that the true danger lies at any rate.

They are extremely predatory and will not usually stop until all on board have been attacked, unless they are driven off, or they exhaust themselves attempting to access locked portions of the ship. A certain way to survive them is to simply lock yourself away inside the ship where they have no chance of getting to you before the ship departs the storm. The big problem here is that someone still has to man the helm and tend to other above-deck problems.

The tendrils can move extremely quickly once a chance to strike comes, and they will not hesitate. The tendrils are capable of penetrating only the lightest of armours, but, of course, there is always a chance that they will not strike armour, and given the fact that they will only strike at sea and during a storm, it is not particularly wise to wear heavier armour while fighting them off, lest another danger entirely claim the valiant defender's life.

Additional Information
Gesthari are not strong, but their poison is potent. They are capable of absorbing moderate shocks, but this will not allow them any sort of electrical attack, instead it can merely be thought of as a form of food for them.

Nor are they in particular danger from wind magic, being used to such high velocity winds.

They can of course be damaged by a severe electric shock and more or less anything else that is damaging. They are most susceptible to fire, as they are not at all adapted for it.

They are of course completely immune to their own poison.
Their poison is fast acting, and induces paralysis and commences the shutdown of the body. Several allergenic responses are obvious, including the inability to breathe, severe dizziness, and weeping from the eyes. These occur, of course, whilst in a state of paralysis, and only last a minute or two, finishing in death.

Although they can be hurt by electricity, they are generally safe in storms. This does not mean a lightning strike cannot hurt or kill them, it can and probably will. However, the Gesthari will attempt to absorb the electrical discharges before they can accumulate into a powerful bolt.