Hello! 2 of these are mistakes.
One digit got cut off from the legendary creatures. The sea reek should have 24 RES and the heather-backed whale should have 20 RES.
The headless jotunn is strongest on their mount (the niflmare) as they gain the niflmare’s strength; once unmounted, they’re much weaker (hence the low strength).
Thanks for letting me know about these! I’ll include these fixes in the next PDF update.