We believe from the posts that companions are fixed in Hellcard in single player. We saw that they no longer seemed to change when you finish Level 12 and this is indicated when you get the "Best Friends Forever" artifact [Increase max HP by 1 after each battle survived]. These are screenshots of companion cards. This isn't all of them. We no longer have the time to finish the set. Hope someone beginners will be able to get a better idea of who to choose when playing. I know there is a Wiki maybe someone will put them there eventually.