Without the book capabilities, Pennywise is pretty much a living mindf**k, but is close to powerless against those with a strong will and mental fortitude and control.
You can't use book versions of characters in a movie vs forum, if it was book/movie vs forum sure you could use book and movie versions of the characters but it's only movie characters you can use
I think that pretty much sums everything up. Even for the sake of argument if Pennywise could use all of his abilities against, Voldemort this would be no contest...,book or movie version. It was fear that, Pennywise preyed and fed upon. Pennywise may be able to get inside of, Voldemorts head and use his fears against him but the most that could potentially do is make, Voldemort scared and paranoid. Even in a state of extreme fear and paranoia, Voldemort will still be able to use his magic against, Pennywise and that in return would just make him more confident and break, Pennywises' spell because I don't see how, Pennywise could defend against any of, Voldemorts magic.
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