What is the ruling on praying and delivering sermons in a mosque built by a sorcerer or charlatan, and does praying and delivering sermons in it after a long boycott harm the da'wah (Islamic call)?

There is no harm in praying in a mosque built with dubious money, unless it was built on the basis of division and harm, in which case one should not pray in it. Prayer is permissible in the aforementioned mosque if its Imam is one whose leadership is valid. Praying in this mosque and delivering sermons in it to clarify the truth does not harm the Da'wah ( Islamic propagation), but rather may lead to influencing its congregants.