I think there's a few different definitions of a "nemesis bird" applicable for me! The first and most traditional one is probably Eurasian golden oriole, which is the only species I haven't seen in the Benelux that is seen as "relatively common" in my region - I'm also still missing things like velvet scoter, black kite, corn bunting and twite that belong in that category, but those all still do get flagged as rare in my specific region (and are all not straightforward to see in any given year). I have seen golden orioles in Spain, just never in the Benelux.
A nemesis bird in another definition is probably red-breasted goose, which is a (thankfully increasingly common) vagrant that I've twitched 5 times now and never seen! I did finally end up seeing one this winter, but then it turned out that it had a red ring around its leg, meaning it was an escapee...
A nemesis bird in another definition is probably red-breasted goose, which is a (thankfully increasingly common) vagrant that I've twitched 5 times now and never seen! I did finally end up seeing one this winter, but then it turned out that it had a red ring around its leg, meaning it was an escapee...