Keep in mind that he was the only one Sidious feared bc yoda deflected every attempt that was made to corrupt him.
I think there's something potentially very cool here, but we have to remember that the ability to cause fear is different than being immune to fear yourself. Also, corruption is not fear.
But I do remember what you're saying about GMY being the only Jedi that Yoda feared, so what about ...
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Yoda automatically places Fear on any enemy Darth Sidius for 1 turn at the start of any encounter. Fear is a significant debuff, but it's only against a character that isn't likely to show up among your enemies very often, so I think that would fit well with the theme we're creating. Thanks!