Cloud giant

There's just something so folktale-ish about cloud giants. These aren't creatures that just randomly exist in the world, these are creatures multiple surrounding villages have wildly differing local legends about. They aren't an "appropriately leveled challenge for the player characters to face", they are a story unfolding itself as you witness it. Their divergent alignments also hint at yet even greater mysteries in the background.

A standoff of (literally) gigantic proportions is taking place at the mouth of Durgil's deeps. Two delegations of previously unseen giants have set up camps, and appear to be constantly arguing and bickering. So far, no physical violence has erupted, but if it does, the nearby townships are sure to be the one to suffer. 

If the local mayor's emissaries manage to sneak past the giants and their random bursts of magic, and delve deep into the treacherous caves, what awaits them at the very bottom is another giant, chained to a monolith. The prisoner looks much like his arguing kin above, but appears ancient beyond measure. At his feet, a plaque stands, an engraving in ancient valhallan on it. "The last one who did not choose a side", the text says.

The old giant, if awakened, pleads his finders "not to let the childer find him, for it shall start the war anew".

In the lands of Ledenya, the brothers who dwell above are treated as deities. The two cloud giants - one kind, benevolent and gregarious, the other cruel, sadistic and petty, come and go with the seasons. As summer draws to a close, Dvoryak's castle, a thing of white and gold sitting on soft clouds, sails beyond the horizon, as Kuryak's castle, with its sharp edges and tall spires appears, riding on a storm.
One winter, though, Dvoryak's castle crashes from the skies. With the last remnants of life, the benevolent giant awakens the seed of greatness within four youths of the tribe, and urges them to find a new home for their people, beyond the Shardspire mountains - but time is short, and they must go before Kuryak comes for them.

For ages, it has been common belief that some cloud giants are good and some evil. The truth, however, is that they go through two psychological and physiological phases in their life. Juveniles tend to be more physically imposing, highly territorial and yearn for violence. As they mature, they settle down, become builders, develop the need for humanoid contact, and essentially reinvent their entire personalities.
A group of mercenaries is shocked when a giant, who nearly murdered them early in their careers by trying to feed them to his pet hydra, congratulates them on their latest escapade and calls them for a feast in their honour. While the patriarch himself is bound to be civil, some of his teenage sons might also be present...