You can find the Giant God Scions in Bigby Presents: Glory of the Giants. There is one for each classic type of giant: storm, frost, cloud, fire and hill. These creatures are the children of the gods, grandchildren of the giant’s All-father. The scions currently rest in their cradles, waiting for you PCs to come and disturb them.
In combat, they function similarly to the various awakenings of greatwyrms and some of the more powerful creatures from Mythic Odyssey of Theros. The encounter starts out with the scions “cradle”. This cradle is a gargantuan elemental. Each one is appropriate to the type of giant god scion they contain. The are said to be a humanoid form composed I’ve created a token for each of them; there isn’t art for them included in the book. The art is courtesy of Dall-e. And yes, I made the hill giant one a little silly. Hill giants are silly.
Giant God Scion, Freed!
When the cradle is defeated, the giant god scion it contains continues the battle. Of course, perhaps you players will try talking to them, and maybe deescalate things? You’re right, probably not. I’ve had the chance to use a few of them in combat at this point. I find it a little unfortunate that they don’t have legendary actions, and I think they punch a little bit below their weight because of it. That said, they do make a big splash with players, and are fun to run. When they do hit, they hit very hard.