What is the English equivalent for the German idiom "Angstgegner"

Solution 1:

A good English equivalent of Angstgegner is bogey team. Here is a definition from encyclo.co.uk:

Bogey team is British sports slang for a team which usually manages to win despite an apparent weakness.

And here is an extract from the explanation of bogey by one stop english:

Most football clubs have a bogey team, meaning a team that either always beats them or against which they habitually enjoy bad luck, as in "Bolton are rapidly becoming Arsenal’s bogey team".

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Webpages with the term "bogey team" in the title include:

Devising a Game Plan for Germany to Finally Beat Bogey Team Italy

Can Germany overcome its bogey team in Italy?

Gareth Bale: we know Belgium, we might even be their bogey team

Revealed! Your Premier League club's bogey team

I am not aware of a common term for when the Angstgegner is an individual and not a team, although HotLicks' suggestion of nemesis fits pretty well here.