Full disclosure, Kris absolutely should have gotten a saving throw against the Polymorph. But he has enough of an idea of how strong Odin is to know that without Mjolnir's bonuses, he mathematically cannot pass it.
Oh definitely. I'm not a huge fan of it myself (aside from my personal feelings that some things should just be impossible, I'm especially not a fan of the other side of that rule, where a natural 1 is always a failure), but I think under the right circumstances Kevin can and will skew rolls in the player's favor, if not just rule that a 20 is a success.
Unfortunately for Kris, these are not the right circumstances.
Author Notes: