Having thought about it a few days (and played some Shadowdark in the interim) I'm souring on the idea of gnomes being able to polymorph into small animals. If those critters can't see in the dark, they're mostly useless; but if they can see in the dark, that breaks one of Kelsey's foundational principles of the game. The ability to turn into a spider and scout ahead in the darkness is very powerful in 5e -- in Shadowdark, where darkness is a much bigger problem, it might flat-out be broken. It's a good NPC or monster ability but perhaps not a good PC ability.
What do y'all think?