What is the ruling on praying behind an Imam who has a problem with his tongue, issues fatwas without knowledge, dyes his beard black, and there is someone better than him to lead the prayer?

If the Imam commits an obvious grammatical error (lahn jali) in Surah Al-Fatihah due to a speech impediment, such as substituting one letter for another, then there is a difference of opinion regarding the validity of praying behind him. However, if the problem does not lead to such an error, then his imamate is only disliked (makruh). As for dyeing hair black, the fatwa is that it is forbidden. The imamate of someone less virtuous (mafdul) is valid even if a more virtuous person (fadl) is present. And the imamate of a fasiq (open sinner) is valid, according to the more preponderant opinion, though disliked.