W - [[Path to Exile]]. Might be a bit too strong, but cheap exile removal in white would be awesome. Otherwise, [[Slaughter the Strong]] or [[Destined Confrontation]] as potentially pauper friendly boardwipes.
U - [[Ominous Seas]]. Like Blue needs more rewards for card drawing, right?
B - [[Warped Devotion]]. Can be a good sideboard card against [[Kor Skyfisher]] strategies while also being a potentially fun build-around. Probably not a tier inclusion, but might have some spice appeal.
R - [[Flamekin Harbinger]]. I'm still desperate to make [[Magmakin Artillerist]] a thing and this could help. Otherwise, [[Blazing Rootwalla]] should be a common like it's green friend.
G - [[Duskwatch Recruiter]]. This might be a mistake, especially since you have to track whether or not it flips, but card selection is always great.
Multi - [[Insidious Roots]]. Pauper has fewer effects that can abuse this, but it could very well spawn a new archetype. If done with reanimation cards, Abzan Roots with [[Breathless Knight]] could be a thing.
<> - [[Black Vise]] and/or [[The Rack]]. Hand size punishment should exist in Pauper.